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.
I just found source tree myself and really enjoy it. The best feature for me is how it allows you to view diffs of all your changes as you write your commit message, that makes it easy to include good detail on all changes.
Also, it's great that Source Tree supports multiple projects. I tried Tower a while ago and it only allowed you to have one project open at a time. Maybe that's changed now, but it's also not free.
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.