WotC Books for D&D:
Savage Species
Dragon Compendium volume 1
Expanded Psionics Handbook
Complete Psionics
Oriental Adventures
Unearthed Arcana
Tome of Magic
Magic of Incarnum
WotC Books for D20 Modern:
Urban Arcana
3rd party books for D&D:
Book of the Righteous (Green Ronin)
Book of All Spells (Fast Forward Entertainment)
Hyperconscious (Malhavoc)
3rd party books for D20 Modern:
Modern Magic
Other 3rd party D20 games/supplements:
Mutants & Masterminds
Nyambe (Atlas)
Northern Crown (Atlas)
Arcana Unearthed/Evolved (Malhavoc)
Midnight 2Ed
Swashbuckling Adventures
Iron Heroes (Malhavoc)
Spycraft 2.0
Arsenal
Forge
Second World
Other systems:
HERO 5th
Deadlands
Space 1889
Godlike
Paranoia XP
Traveller (any version)
Shadowrun
Call of Cthulhu
GURPS
Spaceship Zero
RIFTS (basic book only)
Not all of the games have good systems- some dislike of RIFT's system is to be expected- but they have excellent concepts that could inspire others. Others, like HERO or GURPS are flexible enough to model a wide variety of games with just one book. I suggested Paranoia XP because the new rules cover both comedic role-play and a serious game, all in one package.
Savage Species
Dragon Compendium volume 1
Expanded Psionics Handbook
Complete Psionics
Oriental Adventures
Unearthed Arcana
Tome of Magic
Magic of Incarnum
WotC Books for D20 Modern:
Urban Arcana
3rd party books for D&D:
Book of the Righteous (Green Ronin)
Book of All Spells (Fast Forward Entertainment)
Hyperconscious (Malhavoc)
3rd party books for D20 Modern:
Modern Magic
Other 3rd party D20 games/supplements:
Mutants & Masterminds
Nyambe (Atlas)
Northern Crown (Atlas)
Arcana Unearthed/Evolved (Malhavoc)
Midnight 2Ed
Swashbuckling Adventures
Iron Heroes (Malhavoc)
Spycraft 2.0
Arsenal
Forge
Second World
Other systems:
HERO 5th
Deadlands
Space 1889
Godlike
Paranoia XP
Traveller (any version)
Shadowrun
Call of Cthulhu
GURPS
Spaceship Zero
RIFTS (basic book only)
Not all of the games have good systems- some dislike of RIFT's system is to be expected- but they have excellent concepts that could inspire others. Others, like HERO or GURPS are flexible enough to model a wide variety of games with just one book. I suggested Paranoia XP because the new rules cover both comedic role-play and a serious game, all in one package.