For a while now I've known about ack, the slick grep substitute written in Perl. And I've known that the multi-file search function in TextMate was lousy, slow and memory-eating.
What I didn't know was that there was an Ack bundle for TextMate. It is a dream come true as far as I'm concerned. Okay, I've only briefly played with it, but it's screamingly fast and produces good-looking results. If there's a better add-on for TextMate, I don't know about it.