http://www.youtube.com/watch?v=cyyuqf1m-2E
For a moment, it made me want to ditch Windows and migrate to Mac just to use this client.
Personal favorite, being able to see up stream commits without actually applying them on your local branch.
I currently use SmartGIT on Windows and I am sort-of-happy with it. I wonder why no one is trying to create a killer Git client on Windows.
I'd bet the majority of Windows developers use Microsoft technologies, preferring TFS over Git. While there are less Mac users, they're all your target market.
Because there is already one: SourceTree (which is also available for OS X).
(I don't know why the Windows incarnation lacks a tree view. A Win32 treeview would be perfectly functional, and they're easy to code for. (Never having seen the SourceTree code, I can of course confidently say that this would apply here.) But if you don't mind a flat list, Reveal Log... is present and correct. So you'd be good to go already.)
There is SourceTree, which is already quite feature-rich and stable.