Subversion

Cornerstone is a Mac OS X SVN client. I can tell you that this app is awesome!

The interface takes a number of UI cues from iTunes by using one window. The one window interface is much more efficient on a laptop. You do have the option in preferences to switch to a multi window mode.

I am a big fan of subverison. I current use a combination of TextMate, ZigVersion and command line SVN to work with Subversion for my University development at UNC Charlotte.