I tried a few before settling for http://www.draw.io/[^]. It's browser based, it integrates well with google drive/docs and does other kinds of diagrams pretty good too.

Now now, posting comments is cheating, we were talking about commit messages! But since we're on that train, I've seen production code with the following gems: 'Delete this after share-out! 'Start here on friday aaaand: 'God help us all