RPGArchive

Archive of adventures categorized by genre and system. Accepts submissions.
http://www.rpgarchive.com/

The RPG Character Mortuary

Final resting place for characters who died - tragically or otherwise - in roleplaying games. Accepts submissions.
http://www.electricferret.com/mortuary/

Neonflux

100+ character sheets for many systems in PDF and TIFF format, plus adventures for D&D and Palladium.
http://neonflux.tripod.com/

RPG Sheets

Over 700 character sheets from over 200 game systems, including official sheets, custom and WebRPG.com sheets. Accepts submissions.
http://www.rpgsheets.com/

The Keep

A large collection of files, mostly related to RPGs: systems, rule supplements, information about or for campaign settings, adventures and ideas for adventures, other GM aids, fiction, humour, and miscellaneous RPG material.
http://keep.trawna.com/

RPG Hoard - downloadable resources

Some adventures, fonts, maps, monsters, programs, and other resources for some systems.
http://www.rpghoard.com/

The Dragons' Den

Netbooks, adventures, and character graveyards for D&D, West End's Star Wars, and the World of Darkness.
http://www.geocities.com/quizzy_the_quick/

The Harrow

Former roleplaying guide Dru Pagliassotti's archive of articles on roleplaying, gamemastering, and adventure writing.
http://www.theharrow.com/rpg/

Docufluff

Articles, essays, and game journals on multiple games.
http://www.night-sky.org/~spotty/writing/docufluff.html