I've been using GitX for months and it's pretty good, but it still buggy at times. I've been using the GitX (L) fork, since the original GitX doesn't seem to be actively maintained anymore. It's available here: http://gitx.laullon.com/

A few days ago a co-worker turned me on to SourceTree (http://www.sourcetreeapp.com/), which is also free and developed by Atlassian. I've got to say it's a bit more polished and so far it looks like it might be replacing GitX for me.