I ran into a problem using the HTMLDiff code found in i2 for doing nice diffs in Ruby. Of course, you’ll probably want to use in Rails, but if you are running Rails 2.1 (or maybe even other versions), you’ll want to use an updated version instead.

Update: It looks like this HTMLDiff code is no longer available at the provided links. I think I still have a copy somewhere, let me know if you need it by leaving a comment.