SourceTree is frequently recommended on Stack Overflow, has good reviews on the App Store, and seems to tie with Tower for Mac Git GUI of choice.

Atlassian, maker of cost-hosting service Bitbucket, has acquired SourceTree, a Mac client for Git and Mercurial distributed version control systems and Subversion source control.

The company’s offerings are used by 26,000 customers around the world, including Facebook, Zynga, Cisco, and Adobe. SourceTree helps manage repositories from Git and Mercurial DVCS systems.