7 links
Feed Validator for Atom and RSS
feedvalidator.org
This is a validator for syndicated feeds. It works with RSS 0.90, 0.91, 0.92, 0.93, 0.94, 1.0, and 2.0. It also validates Atom feeds.
Feedvalidator-users Email List
lists.sourceforge.net
Questions, bugs, patches, and general discussion of FeedValidator.org's Atom and RSS feed processing service.
Redland RSS 1.0 Validator and Viewer
librdf.org
Enter the address of an RSS 1.0 feed into the form, and it will be validated and formatted for display.
W3C RDF Validation Service
3.org
A full RDF Validation Service - for use with any RDF, not just RSS 1.0
Will the real RSS validator please stand up? [dive into mark]
diveintomark.org
Elaborates on how the RSS community is in disagreement about the exact format for RSS feeds and individual entries.