The standard git-gui and gitk tools, bundled with git, are much better than nothing, but at the same time not much to look at compared to some other GUIs. It's a shame that these tools have seen almost no considerable improvement in the last few years, as a good cross-platform GUI bundled with git would certainly be great. Perhaps that is due to the fact that they're written in Tcl/Tk, so the codebase is not easily approachable.

I've tried a few third-party GUIs such as SmartGit (now SmartGitHg), git-cola and Git Extensions, but they all lacked in one area or another and drove me back to the standard ones. Looking forward to trying SourceTree.