This problem begged a simple solution, so I’ve created FeedSifter.com. It is a very easy to use service that allows you to monitor any RSS/RDF/Atom feed for multiple different groups of words. FeedSifter automatically determines what sort of feed you are filtering and gives you only the entries that you care about. You can generate as many filtered feeds as you’d like, and you can change your filter at any time by returning to the site.
For example, say you want to filter the FatWallet.com Hot Deals feed for free items, NewEgg.com deals, and drives of all sorts (USB, harddrives, etc). You could use a filter like the following:
Once entered, you are provided with a filtered feed URL and you’re all set.