This issue has been coming up fairly regularly since the omnibus editions first came out, so I thought it was about time we compiled a complete list of the comics contained in each volume. To get the ball rolling I'll start with the entries from the volumes I already have. After that, those of you who are fortunate enough to own more can post your own and I'll update the list.
Please note that I'm only looking for people who actually physically have the volumes, and can verify the contents personally. If you could list the contents in the order it appears it would also be much appreciated.
Aliens Omnibus: Volume 1
- Outbreak (#1-6)
- Nightmare Asylum (#1-4)
- Female War (#1-4)
- Theory of Alien Propagation (DHP #24)
- The Alien (DHP #56)
Aliens Omnibus: Volume 2
- Genocide (#1-4)
- Harvest (Previously Aliens: Hive #1-4)
- Colonial Marines (#1-10)
Aliens Omnibus: Volume 3
- Rogue (#1-4)
- Sacrifice (one-shot)
- Labyrinth (#1-4)
- Salvation (one-shot)
- Advent/Terminus (DHP #42-43)
- Reapers (DHP Fifth Anniversary Special)
- Horror Show (DHC #3-5)
Aliens Omnibus: Volume 4
- Music of the Spears (#1-4)
- Stronghold (#1-4)
- Frenzy (#1-4 - Previously Aliens: Berserker)
- Taste (one-shot)
- Mondo Pest (one-shot)
- Mondo Heat (one-shot)
Aliens Omnibus: Volume 5
- Alchemy (#1-3)
- Kidnapped (#1-4)
- Cargo (DHC #15-16)
- Survival (#1-3)
- Alien (DHC #17-19)
- Earth Angel (one-shot)
- Incubation (DHP #101-102)
- Havoc (#1-2)
- Lovesick (one-shot)
- Lucky (Decade of DH #3)
Aliens Omnibus: Volume 6
- Apocalypse: The Destroying Angels (#1-4)
- Once in a Lifetime (DHP #140)
- Xenogenesis (#1-4)
- Headhunters (DHP #117)
- Tourist Season (DHC Annual 1997)
- Pig (one-shot)
- Border Lines (DHC #121)
- 45 Seconds (Aliens: Special)
- Elder Gods (Aliens: Special)
- Purge (one-shot)
- Glass Corridor (one-shot)
- Stalker (one-shot)
- Wraith (one-shot)
Aliens versus Predator Omnibus: Volume 1
- Aliens vs. Predator (#1-6)
- Blood Time (one-shot - Previously AVP: War #0)
- Duel (#1-2)
- War (#1-4)
- Eternal (#1-4)
- Old Secrets (AVP Annual #1)
- The Web (DHP #146-147)
Aliens versus Predator Omnibus: Volume 2
- Deadliest of Species (#1-12)
- Booty (one-shot)
- Hell-bent (AVP Annual #1)
- Pursuit (AVP Annual #1)
- Lefty's Revenge (AVP Annual #1)
- Chained to Life and Death (AVP Annual #1)
- Genocide (#1-4 - Previously AVP: Xenogenesis)
Predator Omnibus: Volume 1
- Concrete Jungle (#1-4)
- Cold War (#1-4)
- Dark River (#1-4)
- Rite of Passage (DHC #1-2 - Also Predator: Jungle Tales)
- The Pride at Nghasa (DHC #10-12 - Also Predator: Jungle Tales)
- The Bloody Sands of Time (#1-2)
- Blood Feud (DHC #4-7)
Predator Omnibus: Volume 2
- Big Game (#1-4)
- God's Truth (DHP #46)
- Race War (#1-4)
- The Hunted City (DHC #16-18)
- Blood On Two-Witch Mesa (DHC #20-21)
- Invaders From The Fourth Dimension (one-shot)
- 1718 (Decade of DH #1)
Predator Omnibus: Volume 3
- Bad Blood (#1-4)
- Kindred (#1-4)
- Hell and Hot Water (#1-3)
- Strange Roux (one-shot)
- No Beast So Fierce (?)
- Bump In the Night (?)
Predator Omnibus: Volume 4
- Primal (#1-2)
- Nemesis (#1-2)
- Homeworld (#1-4)
- Xenogenesis (#1-4)
- Hell Come a Walkin' (#1-2)
- Captive (one-shot)
- Demon's Gold (DHP #137)