Feedmil is a search engine for RSS feeds. It does this specific task very, very well. Search for feeds relating to any keywords you wish, and modify your results using a set of slides that emphasize/de-emphasize words that show up in your results.
I wish they had a more detailed “about” page, especially information on how they determine popularity, authority, quality, and relevance.
found via RSS4Lib
Update on feedmil: After its first launch as a topical feed search engine in last April, feedmil.com is fully redesigned and enhanced to go real-time.
It is now a real-time search engine for a variety of live streams from blogs, microblogs, podcasts, as well as public and social media.
Please come and enjoy!