Corporate Sites

Iron Crown Enterprises
Eidolon Studios (Shadow World)
Alderac Entertainment Group (Legend of the Five Rings, 7th Sea, Spycraft, Stargate)
BITS (Traveller)
Brittannia Game Designs (Chivalry & Sorcery)
Forgotten Futures
Malefex (Principa Malefex)
Malhavoc Press & Monte Cook
Necromancer Games (d20 System-compatible products)
Pelgrane Press (Dying Earth RPG)
ProFantasy Software (Campaign Cartographer)
NBOS Software (Fractal Mapper, Character Sketcher)
Character Software Companion
Steve Jackson Games (GURPS, Illuminati, Car Wars, etc.)

Magazine Sites

Other Hands Magazine (paper-based)
Games Unplugged (paper & online)
Places To Go, People To Be
Pyramid Online

d20 System & Open Gaming Sites of Interest

Open Gaming Foundation
The Open Gaming Exchange
Dominion Games

Sites of Interest

ICE Games Mailing List Archives
Lords of Conquest (Free online: Medeival Diplomacy, Dragonlords!, Galactic Warlords)
RPG Resource Masters (RM, Spacemaster, HARP content)