Since this question was first posted, an Android app has been added to the market that can checkout Git repos, called Agit. It can’t commit or push yet, but the clone/fetch/pull functionality is useful. The other issue is that a patched version of ConnectBot needs to be installed before Agit if you want to use SSH keys. If you already have ConnectBot, uninstall it first. I did not do this and ran into problems.
Edit: As of April 2021, the ability to push and pull has been added, however, it does seem to be very buggy as I have only been able to pull changes, but never push them.