The Tao of Mac
ShiftIt is a keyboard-based tiling window helper for the Mac that can position windows on a corner or half of a screen (with passable support for multiple displays, better if they are the same size) using keyboard commands. Although not as powerful as X tiling window managers and (as of this writing) lacking configurable hotkeys, it is fast and efficient to use for arranging multiple windows.
I have recently taken upon myself to maintain a fork to which I’ve added a few enhancements and that has proven somewhat popular among my colleagues at SAPO.