Discussion forums and resources
A. Long-running homebrewing mailing list covering mainly advanced topics. Can seem like science graduate school at times, but an incredibly valuable resource going back nearly 20 years, and the source of a wide variety of now-common homebrewing practices.
B. An active newsgroup with a deep archive on Google.
C. Some other forums with quality information.
D. Site started by r.c.b participant Alan McKay, it has grown into its own forum and resource.
Note: Many of the homebrew shops listed above have discussion boards - Northern Brewer and Morebeer definitely do.
Books
http://www.beerbooks.com is a tremendous resource. Prices seem to be in the same range as Amazon.