WinSplit allows you to quickly move windows to your other screen and arrange windows. This feature is great if you work with a lot of windows or need to utilize all that space you have. Simply press Crtl, Alt and Left or right and your current window will move to the respective window. You can also hold Ctrl and Alt and drag windows to specific locations to get the same Use the same Ctrl, Alt and and the number pad and the window will be positioned based on the number pressed.
The only issues I have encountered has been integration with other apps that use Ctrl and Alt combos. A few apps I've had problems with are Photoshop and Texter. You can always customize keystroke settings to resolve these issues..
Windows 7 includes some of the features, but I think WinSplit really polishes these features.