Here are some current books on RSS.
Syndicating Web Sites with RSS Feeds For Dummies by Ellen Finkelstein
Developing Feeds with Rss and Atom by Ben Hammersley
RSS for Educators: Blogs, Newsfeeds, Podcasts, and Wikis in the Classroom by John G. Hendron
RSS and Atom in Action: Web 2.0 Building Blocks by Dave Johnson
Beginning RSS and Atom Programming by Danny Ayers
Secrets of RSS by Steven Holzner
RSS and Atom: Understanding and Implementing Content Feeds and Syndication by Heinz Wittenbrink
Blogging and RSS: A Librarian’s Guide by Michael P. Sauers
Beginning XML, 4th Edition (Programmer to Programmer) by David Hunter
Full details on the books here:
RSS Books