I just found feed rinse. Seems like a nice site, good look and feel.
The feature list is here. The keyword include/exclude design is excellent. We have had requests for combination keywords (which sort of corresponds to their "filter only if all criteria are met" tick box) but I wanted to make a note of this because it's a good interface – and because it shows that this space is getting filled rapidly.
Their feed rinse blog is here.
Another RSS filter is here: ZapTXT
I really like the graphic logo for FeedBlendr