Side-by-side diff and patch visualization

Does anybody know of any tools for doing side-by-side visualizations of diffs and patches which work well with Git?

By side-by-side I mean something like what's shown in this screen shot:

<http://wincent.com/images/side-by-side-diff.png>

For simple diffs there is little advantage here over a raw textual diff, but as patch complexity and size increase the side-by-side diff can sometimes prove itself to be more useful:

- totally flexible notion of context (you can scroll as far as you  
want in either direction)

- this flexibility comes with the same rapid movement between changes  
(ie. up/down cursor keys to jump between hunks no matter how far  
apart they are)

- for complex diffs, truly comprehending the nature of the changes  
may be easier in a side-by-side format

- as icing on cake, the implementation in the screenshot highlights  
the removed/added portions within each line

Now, that screenshot is actually of Apple's FileMerge app on Mac OS X and it would be fairly straightforward to write a dump wrapper script that either just interpreted the output of git-diff, or could be used in conjunction with GIT_EXTERNAL_DIFF, to feed files into opendiff two at a time, but that wouldn't allow you to easily visualize diffs which touch many paths.

So, can anyone recommend a tool which can do this kind of side-by- side visualization and plays nicely with Git? Experience with opendiff and git-mergetool has spoilt me here. For most cases I would continue to use vanilla git-diff (or gitk), but when I see a change that I'd like to visualize side-by-side I'd like to be able to use this alternative diff viewer (or can gitk already do side-by-side diffs and I just haven't seen how to turn them on?). Bonus points if I could not only view existing commits, but proposed commits too (ie. the ability to feed in a patch and see a side-by-side visualization of what the diff would look like if applied).

If nothing exists I will look at quickly hacking something together (most likely something that just reads the output of git-diff), but it will be just that, a quick hack.

Cheers, Wincent