CBS.com: Numb3rs
Official network site. Includes show overview, cast information, and interviews.
http://www.cbs.com/primetime/numb3rs/

IMDb: Numb3rs
Cast, crew, and production information.
http://www.imdb.com/title/tt0433309/

Numb3rs
Fan fiction, episode guide, and information on using numbers to solve crimes.
http://www.redhawke.org/numb3rs/numb3rsindex.html

Numb3rs Never Lie
Screen captures, video clips, image gallery, episode guide, and news.
http://www.fan-sites.org/numb3rs/

NUMB3RS.org
Schedule, news, spoilers, image gallery, message board, cast information, and downloads.
http://www.numb3rs.org/

Yahoo! Groups : Numb3rs RPG
Members participate in a role-playing game based on the series. [Yahoo! registration required.]
http://games.groups.yahoo.com/group/Numb3rs_RPG/