Lifehacker has a great greasemonkey script to add filtering support to your Google Feed Reader, with full regex support (if you go that way).

“automatically highlights any items in Google Reader whose contents match any word in your matchlist. The script’s filtering does not remove posts from Reader, so you won’t miss any content—you’ll just have your attention drawn more closely to the matching items with the highlighting (though clearly a toggle option to truly filter matches would be useful). Google Reader Filter is free to install, requires Firefox with the Greasemonkey extension”

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