Windows XP users have no idea what they are missing from Windows 7: Aero Snap! Press the Windows key and the windows snap to the borders of the screen or even over screens!
This tool installs similar shortcuts on Windows XP (but not for the windows key (yet))
CTRL + ALT + LEFT: dock active window to the left half of the screen
CTRL + ALT + RIGHT: dock right
CTRL + ALT + UP: dock upper to upper half of screen
CTRL + ALT + DOWN: dock to lower half
CTRL + ALT + SHIFT + UP: maximize active window
CTRL + ALT + SHIFT + DOWN: Reset to normal size