BetterSnapTool is a utility that mimics Windows 7 Aero snap, allowing you to easily manage your window positions and sizes by either dragging them to one of your screens corners or to the top, left or right side of your screen. This lets you easily maximize your windows or position them side by side.
In addition to that you can set keyboard shortcuts in order to move and resize your windows the way you want.
BetterSnapTool supports multiple monitors, hidden dock etc. You can change the design of the preview window and even set application specific snapping sizes!