Archives

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

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

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/

Neonflux
Over 100 character sheets for systems in PDF and TIFF format, plus adventures for Dungeons and Dragons and Palladium.
http://neonflux.tripod.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/

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

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