I wanted an RSS filter because BlogLines doesn't have one, but I couldn't find anything suitable. So: ReFilter.
It uses simple filters modelled on Google syntax, e.g.:
exploded-"sars art"dccreator:bob-start:title:"re:"has:enclosureenclosure:type:audio/mpeg-enclosure:url:aol-category:politics -category:ranting-(category:politics OR category:ranting)Or even something a little more complicated: -"BoingBoing friend" -"former guestblogger" -"reading from my" -ukulele -Disney -((RIAA OR MPAA OR DRM OR copyright) AND (fascist OR Nazi)) -dccreator:Xeni
Real world example: I'm using -title:"best of win" to filter out those "Best of Weblogs, Inc." features, which are ridiculously frequent on low-volume blogs -- there's some amusing irony in cluttering the Spam Weblog with three in a row.
Anyway, give it a spin.