A subtle little addition has been made to the Google AJAX Feed API:

The AJAX Feed API makes it easy to display RSS and Atom feeds on any web page. Unfortunately, its not always quite as easy to find the feed URL of the feed that you wanted. To help with discovering and finding feeds, today we launched two additional methods. The new findFeeds() method searches for feeds based on a simple query. The new lookupFeed() method accepts a url and then returns to you the primary feed associated with that URL. We have put together some nice samples (findFeeds sample, lookupFeed sample) to get you started.