Tbone's GURPS Diner

The home of an enormous stew of GURPS variants and expansions, most notably "GURPS Gulliver," which begins by adressing issues of scale and goes on to re-tool half the system for sharper performance.
http://www.io.com/~tbone/gurps/

Roleplayer: The GURPS Magazine

An online archive of articles, adventures, and features from the sadly out-of-print SJ Games magazine/newsletter devoted entirely to GURPS. The complete (text) contents of the magazine's paper run is present.
http://www.sjgames.com/gurps/Roleplayer

GURPS: Generic Universal Roleplaying System

The official Steve Jackson Games page for GURPS. Features news on new and upcoming releases, and links to the massive SJ Games library of online resources.
http://www.sjgames.com/gurps

GURPS Lite

A distilled, complete version of the GURPS Basic Set in 32 pages, available as a free download. Designed both for newcomers to GURPS and as a tool for experienced GMs to teach the game to others.
http://www.sjgames.com/gurps/lite/

GURPS Character Repository

A collection of characters, adventures, house rules and links. By SD Anderson.
http://www.geocities.com/TimesSquare/Dungeon/5264

Blue Room GURPS

A large collection of "classic era" GURPS articles, adventures, design notes, and product ratings by S. John Ross, author of GURPS Warehouse 23 and other supplements. Includes the Unlimited Mana rules.
http://www.io.com/~sjohn/gurps.htm

GURPS Stuff by Scott Maykrantz

A collection of articles, rules, and notions from the keyboard of Scott Paul Maykrantz, author of GURPS Creatures of the Night.
http://www.omnology.com/om-gurps.html

Ebon Tower Fantasy Gaming

A general-purpose fantasy gaming webzine with a strong GURPS slant. Site includes templates, revised rules, and a campaign setting.
http://www.telisphere.com/~davidl

GURPS Frequently Asked Questions

The official FAQ maintained by Steve Jackson Games.
http://www.sjgames.com/gurps/faq/

Dreambird's Lair

A broad collection of articles, characters, rules, equipment, adventures and settings for use with GURPS.
http://www.gurpsmaster.de

Rare GURPS Items

Incanus' collection of scraps, tidbits, articles, and variants - dozens of GURPS items, including original work and articles culled from Usenet and sundry sources.
http://www.thecabal.org/gurps/rareitems/

Fantasy Geographic Society: GURPS

An assortment of GURPS options and articles, with links to several others.
http://fantasy.geographic.net/gurps/

The Krommnotes

An extensive collection of rulings for GURPS by Sean "Dr. Kromm" Punch, the GURPS Line Editor.
http://www.krommnotes.org

DM's GURPS Page

Quite a number of articles, including tech discussions, rules articles, adventures & seeds, and the Amber Nebula SF campaign.
http://www.dangermouse.net/gurps/

GURPSnet

Mailing list on GURPS with archive of vehicles, gear, characters and adventures.
http://gurpsnet.sjgames.com/

MOD-RPG

New and altered rules for GURPS campaigns.
http://modrpg.lab.pro.br/

GURPS WebWorlds

Coordination site for a number of game worlds for the GURPS system.
http://www.picotech.net/gww/

Brandon Cope

Vehicles, characters and campaign settings for GURPS and Traveller.
http://www.geocities.com/copeab/

GURPSWiki

Articles on general GURPS topics.
http://www.gurpswiki.net/