This one is intriguing, Feed Rinse allows you to define your RSS feeds, define filters, and then access a single filtered RSS feed. The tag line proclaims it “like a spam filter for your RSS subscriptions”, and while the inspiration seems to have been profanity filtering, this seems like a useful service (and one that will undoubtedly get acquired shortly).
I would like to invite you to check out zaptxt.com. It’s an RSS
filtering and notification application that I wrote about a year ago.
For each RSS feed I can specify keywords (by using Boolean logic) that I
am interested in and the program will ping the feed every so often and,
if it finds that the new RSS post contains my search keywords, it will
send me a notification via email or SMS or IM. There’s no limit to the
amount of filters you can setup. I would appreciate if you checked out
zaptxt.com and let me know what you think.