APML allows users to share their own personal Attention Profile in much the same way that OPML allows the exchange of reading lists between News Readers.
Love Digg's RSS feed but don't have time to keep up with it all? Disstill is like your regular Digg RSS feed but filters out stories below the minimum diggs that you set.
By filtering your results by popularity, you'll be able to pare down a bunch of results that are presumably all relevant into the top sites on your topic, or some surprising ones you might not have heard of.