Slate: Tiling window management for OS X
If you prefer something a little more simple, Spectacle is a free program similar to ShiftIt and SizeUp. Basically it's shortcuts to put windows in any half or quarter of your screen, centered, maximized, or send to other monitors.On the app store: http://itunes.apple.com/us/app/spectacle/id487069743?mt=12(I have no affiliation with this program. But I like it.)