Summary: A short review of Mac Git GUI clients.
I basically just deleted my old version of this Mac Git GUI client article, as it quickly became out of date. In short, the only Mac Git GUI I can recommend at this time is a product named SmartGit. Other Mac Git GUI clients like GitNub seem to have died; and I can't recommend gitk or Git GUI, as both of those seem like Git repository browsers as opposed to true Git clients. This is a bummer, as I will always recommend a good open source tool before a similar commercial tool.
(I previously wrote that I thought GitX might be dead/dying, but it's not. See the comment and URL in the Comments section below.)
The best Mac Git GUI client of 2011: SmartGit
On the other hand, SmartGit lets you do many of the things you'll need to do with Git on a regular basis, including push, pull, work with branches, view changes with log, etc.
The only downfall with SmartGit is that it's a commercial product, and $69 per user (less per user for multiple users). However, on the positive side, if you're working on a non-commercial project, you can use SmartGit free of charge.
While gitk or git gui might work for developers, as I look at starting a new company and think about working with web designers and other people who don't work regularly at the command line, SmartGit looks like the only Mac Git GUI we'll be able to use right now.
Other possible Mac Git GUI clients
Since rewriting this article yesterday, I've received several comments here and on Twitter about other possible Mac Git GUI clients. I haven't yet taken the time to test them, but since I've opened the door to linking to commercial applications, ok, here goes: