I needed this list myself, so I thought it might be useful for my readers as well. Here is a list of all the DC Showcase Presents volumes and the issues/stories they reprint:
Adam Strange V1: Showcase 17-19, Mystery In Space 53-84 (Adam Strange stories only).
Ambush Bug V1: DC Comics Presents 52, 59, 81, Supergirl 16, Secret Origins 48, Action Comics 560, 563, 465, Ambush Bug 1-4, Son of Ambush Bug 1-6, Ambush Bug Stocking Stuffer 1, and Ambush Bug Nothing Special 1.
Aquaman V1: Adventure 260-280, 282, 284 and Detective 293-300, Lois Lane #12, Jimmy Olsen #55, World's Finest 125-129, (Aquaman stories only) Showcase 30-33, Aquaman 1-6.
Aquaman V2: Aquaman 7-23, World's Finest 130-133, 135, 137, 139 (Aquaman stories only) and Brave & Bold 51.
Aquaman V3: Aquaman 24-39, Brave & Bold 73, Jimmy Olsen 115 (Aquaman story only).
Atom V1: Showcase 34-36, and Atom 1-17.
Atom V2: Atom 18-38, Atom-Hawkman 39-45 (Atom stories only).
Batgirl, V1: Detective Comics #359, 363, 369, 371, 384, 385, 388, 389, 392, 393, 396, 397, 400, 401, 404, 405-424, Batman #197, Adventure Comics #381, World's Finest Comics #169 and 176, The Brave and The Bold #78, Justice League of America #60 and Superman #268 and 279.
Batlash: Showcase 76, Batlash 1-7, DC Special Series 16, Jonah Hex 49, 51-52.
Batman and the Outsiders: Batman and the Outsiders 1-19, Brave & Bold 200, New Teen Titans #16.
Batman V1: Detective Comics 327-342 (Batman stories only) and Batman 164-174.
Batman V2: Batman 175-188 (not including annuals 176, 182, 185 and 187) and Detective 343-358 (Batman stories only).
Batman V3: Detective 359-375 (Batman stories only), Batman 189-192, 194-198 and 199-201.
Batman V4: Batman 202-215, Detective 376-390 (Batman stories only).
Blackhawk V1: Blackhawk 108-127.
Booster Gold: Booster Gold 1-25, Action Comics 594.
Brave & Bold Batman Team-Ups V1: Brave & Bold 59, 64, 67, 69-71 and 74-87.
Brave & Bold Batman Team-Ups V2: Brave & Bold 88-109.
Brave & Bold Batman Team-Ups V3: Brave & Bold 109-134 (109 overlap?)
Challengers of the Unknown V1: Showcase 6, 7, 11 and 12, and Challengers of the Unknown 1-18.
Challengers of the Unknown V2: Challengers of the Unknown 18-37 (18 overlap?).
DC Comics Presents Superman Team-ups: DC Comics Presents 1-26.
Doom Patrol V1: My Greatest Adventure 80-85, Doom Patrol 86-101, and Challengers of the Unknown 48.
Eclipso: House of Secrets 61-80 (Eclipso stories only).
Elongated Man: Flash #112, 115, 119, 124, 130, 134, 138 and Detective Comics 327-371 (Elongated Man stories only).
Enemy Ace: Our Army At War 151, 153, 155, Showcase 57-57, Star Spangled War Stories 138-152, 158, 181-183, 200, Detective Comics #404, Men At War 1-3, 8-10, 12-14, 19-20, Unknown Soldier 252-253, 260-261, 265-267 and DC Special 26.
Flash V1: Stories not specified, but presumed to include Showcase 4, 8, 13-14, and Flash 105-119.
Flash V2: Flash 120-140.
Flash V3: Flash 141-161.
Green Arrow V1: Adventure 250-266, 268-269 (Green Arrow stories only), Brave & Bold 50, 71, 85, Justice League of America 4, and World's Finest 95-140 (Green Arrow stories only).
Green Lantern V1: Showcase 22-24 and Green Lantern 1-17.
Green Lantern V2: Green Lantern 18-37.
Green Lantern V3: Green Lantern 39-59. (Note missing Green Lantern 38?)
Green Lantern V4: Green Lantern 60-75.
Haunted Tank V1: GI Combat 87-119, Brave & Bold #52 and Our Army At War #155.
Haunted Tank V2: GI Combat 120-157.
Hawkman V1: Stories not specified; presumed to include Brave & Bold 34-36, 42-44, and Mystery in Space #87-90, and Hawkman 1-11.
Hawkman V2: Hawkman 12-27, Atom-Hawkman 39-45, Atom 31, and Brave & Bold 70.
House of Mystery V1: House of Mystery 174-194.
House of Mystery V2: House of Mystery 195-211.
House of Mystery V3: House of Mystery 212-226.
House of Secrets V1: House of Secrets 81-98.
House of Secrets V2: House of Secrets 99-119.
Jonah Hex: All-Star Western 2-8, 10-11, Weird Western Tales 12-14, 16-33.
Justice League of America V1: Brave & Bold 28-30, JLA 1-16, Mystery in Space #75.
Justice League of America V2: JLA 17-36.
Justice League of America V3: JLA 37-60 (not including annuals 39, 48, 58).
Justice League of America V4: JLA 61-83 (not including annuals 67, 76).
Legion of Superheroes V1: Adventure 247, 267, 282, 290, 293, 300-328, Action #267, 276, 287, 289, Superboy 86, 89, 98, 117, Superman Annual #4, Jimmy Olsen 72 and 74 (Legion-related stories only).
Legion of Superheroes V2: Adventure 316, 322-348, 365, Superboy 117, 125 and Superman Annual 4. (Seems to be some overlap there with V1).
Legion of Superheroes V3: Adventure 349-368 (365 overlap?) and Jimmy Olsen 116.
Martian Manhunter V1: Stories not specified; presumed to include Detective 225-304 (Martian Manhunter stories only)
Martian Manhunter V2: Detective Comics 305-326 and House of Mystery 143-173 (Martian Manhunter stories only).
Metal Men V1: Showcase 37-40, Metal Men 1-16 and Brave & Bold 55.
Metal Men V2: Metal Men 16-36 and Brave & Bold 66.
Metamorpho V1: Brave & Bold 57-58, 66, 68, Metamorpho 1-17, and Justice League of America 42.
Phantom Stranger V1: Showcase #80, Phantom Stranger 1-21.
Phantom Stranger V2: Phantom Stranger 22-41, JLA 103, House of Secrets 150, Brave & Bold 89, 98.
Robin the Boy Wonder V1: Batman 184, 192, 227, 229-231, 234-236, 239-242, 244-246, 248-250, 252, 254, Detective 386, 390, 394-395, 398-403, 445, 447, 450-451, Jimmy Olsen 91, 111, JLA 50, 91-92, Teen Titans 14, Brave & Bold 83, 100 and World's Finest 195, 200.
Secrets of Sinister House V1: Sinister House of Secret Love 1-4, Secrets of Sinister House 5-18.
Sgt. Rock V1: GI Combat 68, Our Army At War 81-117.
Sgt. Rock V2: Our Army At War 118-148.
Shazam! V1: Shazam! 1-35 (New stories from those issues only)
Strange Adventures V1: Strange Adventures 54-73.
Supergirl V1: Action Comics 252-282, Jimmy Olsen 40, 44, 46, 51-52, Adventure 278, Superboy 80, Lois Lane 14, Superman 123, 139-140, 144.
Supergirl V2: Action 283-321 (missing 282?), (Supergirl stories only).
Superman V1: Superman 122-133 and Action Comics 241-257 (Superman stories only).
Superman V2: Superman 134-145 and Action Comics 258-275 (Superman stories only).
Superman V3: Stories not specified; presumed to be Superman 146-156 and Action Comics 276-292 (Superman stories only)
Superman V4: Action Comics 293-310 (Superman stories only) and Superman 157-167
Superman Family V1: Jimmy Olsen 1-22, Showcase 9.
Superman Family V2: Jimmy Olsen 23-34, Showcase 10, Lois Lane 1-7.
Superman Family V3: Jimmy Olsen 35-44, Lois Lane 8-16.
Teen Titans V1: Brave & Bold 54, 60, Showcase 59, Teen Titans 1-18.
Teen Titans V2: Teen Titans 19-36, Brave & Bold 83, 94, and World's Finest 205.
Unknown Soldier V1: Star Spangled War Stories 151-190 (Unknown Soldier stories only).
Warlord: 1st Issue Special 8, Warlord 1-28.
War that Time Forgot: Stories not specified, presumed to include the Star Spangled War Stories featuring WWII soldiers and dinosaurs.
Wonder Woman V1: Wonder Woman 98-117.
Wonder Woman V2: Wonder Woman 118-137.
Wonder Woman V3: Wonder Woman 138-156.
World's Finest V1: Superman 76, World's Finest 71-111 (Superman-Batman team-up stories only).
World's Finest V2: World's Finest 112-145 (Superman-Batman team-ups only).
World's Finest V3: World's Finest 146-173 (Annuals 161 and 170 not included), (Superman-Batman team-ups only).
Update: Thanks to commenters Lito S and Jim for corrections to the Aquaman and Supergirl entries, and to JJ for going to the trouble to find out all the Batgirl stories!
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Adam Strange V1: Showcase 17-19, Mystery In Space 53-84 (Adam Strange stories only).
Ambush Bug V1: DC Comics Presents 52, 59, 81, Supergirl 16, Secret Origins 48, Action Comics 560, 563, 465, Ambush Bug 1-4, Son of Ambush Bug 1-6, Ambush Bug Stocking Stuffer 1, and Ambush Bug Nothing Special 1.
Aquaman V1: Adventure 260-280, 282, 284 and Detective 293-300, Lois Lane #12, Jimmy Olsen #55, World's Finest 125-129, (Aquaman stories only) Showcase 30-33, Aquaman 1-6.
Aquaman V2: Aquaman 7-23, World's Finest 130-133, 135, 137, 139 (Aquaman stories only) and Brave & Bold 51.
Aquaman V3: Aquaman 24-39, Brave & Bold 73, Jimmy Olsen 115 (Aquaman story only).
Atom V1: Showcase 34-36, and Atom 1-17.
Atom V2: Atom 18-38, Atom-Hawkman 39-45 (Atom stories only).
Batgirl, V1: Detective Comics #359, 363, 369, 371, 384, 385, 388, 389, 392, 393, 396, 397, 400, 401, 404, 405-424, Batman #197, Adventure Comics #381, World's Finest Comics #169 and 176, The Brave and The Bold #78, Justice League of America #60 and Superman #268 and 279.
Batlash: Showcase 76, Batlash 1-7, DC Special Series 16, Jonah Hex 49, 51-52.
Batman and the Outsiders: Batman and the Outsiders 1-19, Brave & Bold 200, New Teen Titans #16.
Batman V1: Detective Comics 327-342 (Batman stories only) and Batman 164-174.
Batman V2: Batman 175-188 (not including annuals 176, 182, 185 and 187) and Detective 343-358 (Batman stories only).
Batman V3: Detective 359-375 (Batman stories only), Batman 189-192, 194-198 and 199-201.
Batman V4: Batman 202-215, Detective 376-390 (Batman stories only).
Blackhawk V1: Blackhawk 108-127.
Booster Gold: Booster Gold 1-25, Action Comics 594.
Brave & Bold Batman Team-Ups V1: Brave & Bold 59, 64, 67, 69-71 and 74-87.
Brave & Bold Batman Team-Ups V2: Brave & Bold 88-109.
Brave & Bold Batman Team-Ups V3: Brave & Bold 109-134 (109 overlap?)
Challengers of the Unknown V1: Showcase 6, 7, 11 and 12, and Challengers of the Unknown 1-18.
Challengers of the Unknown V2: Challengers of the Unknown 18-37 (18 overlap?).
DC Comics Presents Superman Team-ups: DC Comics Presents 1-26.
Doom Patrol V1: My Greatest Adventure 80-85, Doom Patrol 86-101, and Challengers of the Unknown 48.
Eclipso: House of Secrets 61-80 (Eclipso stories only).
Elongated Man: Flash #112, 115, 119, 124, 130, 134, 138 and Detective Comics 327-371 (Elongated Man stories only).
Enemy Ace: Our Army At War 151, 153, 155, Showcase 57-57, Star Spangled War Stories 138-152, 158, 181-183, 200, Detective Comics #404, Men At War 1-3, 8-10, 12-14, 19-20, Unknown Soldier 252-253, 260-261, 265-267 and DC Special 26.
Flash V1: Stories not specified, but presumed to include Showcase 4, 8, 13-14, and Flash 105-119.
Flash V2: Flash 120-140.
Flash V3: Flash 141-161.
Green Arrow V1: Adventure 250-266, 268-269 (Green Arrow stories only), Brave & Bold 50, 71, 85, Justice League of America 4, and World's Finest 95-140 (Green Arrow stories only).
Green Lantern V1: Showcase 22-24 and Green Lantern 1-17.
Green Lantern V2: Green Lantern 18-37.
Green Lantern V3: Green Lantern 39-59. (Note missing Green Lantern 38?)
Green Lantern V4: Green Lantern 60-75.
Haunted Tank V1: GI Combat 87-119, Brave & Bold #52 and Our Army At War #155.
Haunted Tank V2: GI Combat 120-157.
Hawkman V1: Stories not specified; presumed to include Brave & Bold 34-36, 42-44, and Mystery in Space #87-90, and Hawkman 1-11.
Hawkman V2: Hawkman 12-27, Atom-Hawkman 39-45, Atom 31, and Brave & Bold 70.
House of Mystery V1: House of Mystery 174-194.
House of Mystery V2: House of Mystery 195-211.
House of Mystery V3: House of Mystery 212-226.
House of Secrets V1: House of Secrets 81-98.
House of Secrets V2: House of Secrets 99-119.
Jonah Hex: All-Star Western 2-8, 10-11, Weird Western Tales 12-14, 16-33.
Justice League of America V1: Brave & Bold 28-30, JLA 1-16, Mystery in Space #75.
Justice League of America V2: JLA 17-36.
Justice League of America V3: JLA 37-60 (not including annuals 39, 48, 58).
Justice League of America V4: JLA 61-83 (not including annuals 67, 76).
Legion of Superheroes V1: Adventure 247, 267, 282, 290, 293, 300-328, Action #267, 276, 287, 289, Superboy 86, 89, 98, 117, Superman Annual #4, Jimmy Olsen 72 and 74 (Legion-related stories only).
Legion of Superheroes V2: Adventure 316, 322-348, 365, Superboy 117, 125 and Superman Annual 4. (Seems to be some overlap there with V1).
Legion of Superheroes V3: Adventure 349-368 (365 overlap?) and Jimmy Olsen 116.
Martian Manhunter V1: Stories not specified; presumed to include Detective 225-304 (Martian Manhunter stories only)
Martian Manhunter V2: Detective Comics 305-326 and House of Mystery 143-173 (Martian Manhunter stories only).
Metal Men V1: Showcase 37-40, Metal Men 1-16 and Brave & Bold 55.
Metal Men V2: Metal Men 16-36 and Brave & Bold 66.
Metamorpho V1: Brave & Bold 57-58, 66, 68, Metamorpho 1-17, and Justice League of America 42.
Phantom Stranger V1: Showcase #80, Phantom Stranger 1-21.
Phantom Stranger V2: Phantom Stranger 22-41, JLA 103, House of Secrets 150, Brave & Bold 89, 98.
Robin the Boy Wonder V1: Batman 184, 192, 227, 229-231, 234-236, 239-242, 244-246, 248-250, 252, 254, Detective 386, 390, 394-395, 398-403, 445, 447, 450-451, Jimmy Olsen 91, 111, JLA 50, 91-92, Teen Titans 14, Brave & Bold 83, 100 and World's Finest 195, 200.
Secrets of Sinister House V1: Sinister House of Secret Love 1-4, Secrets of Sinister House 5-18.
Sgt. Rock V1: GI Combat 68, Our Army At War 81-117.
Sgt. Rock V2: Our Army At War 118-148.
Shazam! V1: Shazam! 1-35 (New stories from those issues only)
Strange Adventures V1: Strange Adventures 54-73.
Supergirl V1: Action Comics 252-282, Jimmy Olsen 40, 44, 46, 51-52, Adventure 278, Superboy 80, Lois Lane 14, Superman 123, 139-140, 144.
Supergirl V2: Action 283-321 (missing 282?), (Supergirl stories only).
Superman V1: Superman 122-133 and Action Comics 241-257 (Superman stories only).
Superman V2: Superman 134-145 and Action Comics 258-275 (Superman stories only).
Superman V3: Stories not specified; presumed to be Superman 146-156 and Action Comics 276-292 (Superman stories only)
Superman V4: Action Comics 293-310 (Superman stories only) and Superman 157-167
Superman Family V1: Jimmy Olsen 1-22, Showcase 9.
Superman Family V2: Jimmy Olsen 23-34, Showcase 10, Lois Lane 1-7.
Superman Family V3: Jimmy Olsen 35-44, Lois Lane 8-16.
Teen Titans V1: Brave & Bold 54, 60, Showcase 59, Teen Titans 1-18.
Teen Titans V2: Teen Titans 19-36, Brave & Bold 83, 94, and World's Finest 205.
Unknown Soldier V1: Star Spangled War Stories 151-190 (Unknown Soldier stories only).
Warlord: 1st Issue Special 8, Warlord 1-28.
War that Time Forgot: Stories not specified, presumed to include the Star Spangled War Stories featuring WWII soldiers and dinosaurs.
Wonder Woman V1: Wonder Woman 98-117.
Wonder Woman V2: Wonder Woman 118-137.
Wonder Woman V3: Wonder Woman 138-156.
World's Finest V1: Superman 76, World's Finest 71-111 (Superman-Batman team-up stories only).
World's Finest V2: World's Finest 112-145 (Superman-Batman team-ups only).
World's Finest V3: World's Finest 146-173 (Annuals 161 and 170 not included), (Superman-Batman team-ups only).
Update: Thanks to commenters Lito S and Jim for corrections to the Aquaman and Supergirl entries, and to JJ for going to the trouble to find out all the Batgirl stories!
