Plain old `git gui' is worth looking at. Better keyboard support than GitX (though this is not saying much) and the UI for committing lines works better. If I've made a big pile of little changes and I'm trying to split them into multiple commits, I've found git gui way better than GitX.
The history view of GitX is better than `gitk --all', though, and of course having both history and day-to-day duties in the same app is useful.
There is another app called GitY, which I hated immediately. It shows your unstaged changes and your staged changes and your untracked files all in the same window, which I found very confusing, and there doesn't appear to be any way to add individual lines into the index, which is something I do all the time.