Slicer is an invaluable window management app for OS X.
Watch a demo here: http://bit.ly/slicer-demo
Slicer lets you...
... Slice any window to 2/3, 1/3, 1/2, 1/4, 1/8th screen, etc
... Work beautifully on dual-monitor setups
... Mix and match applications in your layou...