Cerebus Comics
Has an encyclopedia of information on the characters, religions, and events comic. And also has a timeline up to Flight.
Cerebus Fangirl Site
Cerebus checklist, pictures, Dave Sim biography, and more than 50 links.
Free Cerebus
Dave Sim and Gerhard give an overview of issues #1 to 136 of the comic.
Melvinbone's Cerebus Page
Large site, with Cerebus fan fiction, a Diamondback page, and other odds and ends.
My World of Comic: Cerebus
Page that focuses on Cerebus' adventures and the other members of the cast.
Yahoo Groups : Cerebus
A mailing list for people who love the comic. Also can be viewed from the webpage.