Xah Lee has a post recommending wgrep, an Emacs extension that allows you to edit the results of grep and have the results reflected in the original file(s). This is good stuff. Although he didn’t write wgrep, Magnar Sveen demonstrates it in his Web Rebels talk. As I’ve said before, this is a great talk and worth watching with or without wgrep.
If you want to see how wgrep works, go watch the talk. I promise you, you want be sorry.