Narth 2000:Bob Schroeck's long-running steam-age fantasy campaign, with everything from cosmology to monetary systems defined.
Dawn of Magic: TL2 world based on ancient Rome, the Third Reich and Tsarist Russia.
Discworld Roleplaying Game: Roleplaying with the world and characters of Terry Pratchett.
DM's GURPS Page: Adventures and campaign settings for GURPS, including additional material for Transhuman Space.
Eric's GURPS Resources: Elfword, Supers and World of Darkness conversions for GURPS.
Ethaliel: A traditional fantasy world for GURPS Fantasy. The site has a collection of characters, some artwork, a diary of the players adventures, as well as maps of towns and villages, and other play aids.
GURPS & RPGs: Contains past campaign stories.
GURPS WWII: Second World War roleplaying game by Gene Seabolt.
Hellboy Sourcebook and Roleplaying Game: Game based on the Mike Mignola comics.
HJO3: Steampunk and modern Greek mythology settings and some characters for Transhuman Space.
IMC - Interstellar Mercenary Corps: A TL9 military/sci-fi campaign world for GURPS.
Northenden: A low fantasy campaign based loosely on Harn.
Saromatia: A fantasy setting featuring a benevolent matriarchy.
The Everdarke Saga: A high-fantasy world with house rules, characters, and monsters. Both an online "worldbook" and a campaign site for the Everdarke group.
Transhuman Space: Roleplaying game set in a future of genetic engineering, artificial intelligence, and nanotechnology by David Pulver.
Transhuman Space Templates: Character templates converted to GURPS 4th edition.
Victorian GURPS: Numerous resources for playing GURPS in a Victorian-era setting. Includes gameworld description, adventure seeds, sample characters, and some house rules.