Lately in my spare time I've been working on adding Git support to Rietveld. (Rietveld is the code review tool that Guido wrote as an App Engine demo. It's similar to Mondrian but open-source and not as tied into Google's workflows. Unfortunately, up until recently it was pretty Subversion-specific, making assumptions like expecting URLs to HTTP-accessible svn repositories. For what it's worth, a likely better system is Review Board; I just think code review is great in general.)
My Rietveld refactoring patch is now in, and we continue to discuss the Git-specific followup. (Thankfully, someone working on Mercurial support already did a lot of the hard initial work.) I've also written a more git-oriented subcommand which works like this: you run git cl upload to put a branch up for review, and git cl dcommit flushes the current branch into a single svn commit using the description from the Rietveld review.