Universal Feed Parser 3.0 (beta 20 of 2004-04-07)
http://diveintomark.org/projects/feed_parser
"It handles Atom feeds, CDF, and the nine different versions of RSS." You can sneer and FUD all you like at Mark Pilgrim's rants on RSS, but he has working code to show for it. (Backed by almost 2000 unit test cases!)