Updated 2001.11.16
Whats a D&D game without an interesting setting? Here is a list of settings people have created and posted online for anyone to use.
A place of magic and legend. A milieu embodying an opulent gamut of arcane wizardry, powerful sorcery, and infamously ruthless overlords. A world once ruled by gods as alien and bizarre as they are mighty. A world ripe for those of staunch resolve, superior cunning, and a mighty sword arm. A world waiting for heroes like you my friend.
(v1.0) A rich history, intrigue, powerful inhabitants, a unique complex of aquaducts, a colossal bronze construct, an extensive complex of thieves tunnels, and more. Comes complete with a full set of color maps. Get your copy of Gateway: The City of Living Waters and be a part of this ongoing campaign setting project.
Greyhawk: the Alternative World is a world that is far more exotic than your standard Greyhawk. There are four Major Powers in the Flanness than normal: the Suloise Empire, the Bakulunish Caliphrate, The Faerie Dominion, and the Lands of the Saurials. Wizardry is a lot more fractured and divided: Sorcery (that wielded by your Standard 3rd Edition Sorcerer), Mystical Elementalism, Fae Magic, Druidic Enchantment, and Diabolism are common forms. Finally, an element of technology will be added: ships and yachts that can skim over water, pains, and sand quite easily will be available. Also, some "magic" items will be items of technology. Check this out, its going to be a fun ride!
Let go for a while and fly with the wings of imagination to the fabulous past. Meet the noble kings, legendary dragons, treacherous thieves, beautiful maidens and all the heroes of legends.
Free realtime online D&D 3e Game
Treyvan is not a campaign setting. It is an online text based D&D game, however, Ifigured this would be the section to list it in. It follows the D&D 3e rules as much as a real time game will allow. It typicaly has from 50 to 100 players logged in at any time. You will need a telnet client to make a character and play the game. I suggest RoAClient.