Aero Snap is a new feature which was added to Windows 7, where in you can drag any window to the top of your screen to maximize it or take it to the left or right to snap it to the side and re-size by 50 per cent and when you drag it back to the last position, the window size will be restored. This feature is now available for XP and Vista. AeroSnap is a simple but powerful application that allows you to resize, arrange or maximize your desktop windows with just drag and drop. Aero Snap supports both Windows XP as well as Vista.
You can see Aero Snap in action in the video below.
The application is currently in beta, so you might get some bugs while using it. You will also need .Net Framework 2.0 or higher for running Aero Snap.