So for anybody that has ever used Trac to look at your SVN repo's you'll know that there is a cool diff tool they use that shows the differences between change sets.
The tool shows the additions / deletions of the code highlighted in different colours with line numbers and some clever shizzle.
It's a pretty simple class which compares and highlights all the differences between 2 files or strings located on your server. I was going to do loads of cool stuff with this but never got round to it. Hopefully his will be a helpful start to someone else.