4 links
.hack//SIGN
dothack.com
Official site by Bandai Entertainment. Story overview, production credits, video releases, trailer, and wallpaper.
.hack//UNIVERSE
geocities.com
Information on all three series', timeline, glossary, and MP3 downloads.
Player Kill
dragonpalace.net
Shrine to Sora, with profile, screen captures, fan art, music, and oekaki board.
Yahoo! Groups: dot-hack-SIGN
groups.yahoo.com
Discussions of the anime series, with archives, songs, and image galleries available to members only.