I haven't yet actually hunkered down and learned TextMate as a key tool like I did when I learned Vim at the sage advice of The Pragmatic Programmer. But I should.
One bit I picked up recently: instead of scrolling through the file drawer to find a certain file in the project, just hit Command-T. Up pops a nice filename search box. Type a key word from the file name, and a list of filenames appears below. Type a little more to shorten the list, or just use arrows and Return, up pops the file. No mouse.
Old hat for many, I'm sure, but for me it makes a big difference.