I just noticed that the app FileMerge (installed with the Developer Tools) is in the Finder services menu now. FileMerge is a very cool app that lets you diff and merge files and directories. I haven't played around with it too much yet, but it shades differences when comparing files, thus making it very easy to see what you're looking at.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020907064656666