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.
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.
What is that all about? It is a service that helps you monitor web sites that do not publish feeds. It will check any web page for updates and deliver them to your favorite RSS aggregator.
PostRank claims to measure social engagement, including blog posts responding to someone else, bookmarking an article, leaving a comment on a blog, or clicking a link to read a news item.