There was no actual series bible. The original writer's guide used to be in the data files at
www.kobol.com
Here's some quick resources:
Battlestar Galactica Original Costume and Prop Museum
Besides photos of original Battlestar Galactica items, check out the series writer's guide, an article about Cylon origins, plus many other features, interviews, and chat transcripts.
http://www.kobol.com (mirrored at
http://www.chrispappas.com ) (Chris Pappas)
Battlestar Zone
Home to the Battlestar Concordance: if there is a Colonial term you want defined or you want the information about any location or people group named in the series: this is the place to go. Also a wealth of other articles and interviews.
http://www.geocities.com/sjpaxton/ (Susan Paxton)
Battlestar Galactica Technical Manuals
Curious about Colonial Fleet ships, weapons, or engine systems? this is the site for you. Explores the "real" science and technology behind the popular TV series, with specs and info on ships, weapons, engines, and of course the Cylons. Also has a nice gallery of CGI BSG art.
http://www.tecr.com/galactica/index.html (Tigerclaws)
Jewels