As a self-confessed source control addict, I found it slightly irritating to say the least that there were no decent apps available which were capable of managing the projects I work on. While there are plenty available with the basic commit/push/pull/branch etc functionality, I couldn't find any decent programs which actually provided a way to track all of your repositories in one GUI, with most preferring to function on a repo-by-repo basis. While this isn't a huge problem, it just adds an extra unnecessary complication to what should be a simple task.
Enter Source Tree: my source control client of choice (works with git, Mercurial and SVN). In addition to being really pretty, it provides all of the functionality you'd expect to find from source control software: branch, tag, merge, rebase, resolve conflicts, stage/unstage files, create and apply patches, view 'blame' reports, view the history of a single file, stash - the list goes on.
Source Tree also integrates nicely with most of the popular diff/merge tools, and provides integration with GitHub, Bitbucket and Kiln hosting services.
Available for Mac OS X for free