Windows only: If you haven’t made the leap to Windows 7 but you’re envious of its awesome window docking and resizing features, grab PowerResizer to bring them to your current version of Windows.
PowerResizer sports a variety of features that make window management easier on XP or Vista. There are keyboard shortcuts for a variety of windows movement and resizing tasks. Pressing keyboard shortcuts while moving a window allows you to dock it to the various edges and corners of your monitor. There are also keyboard shortcuts for resizing windows to various divisions of the screen size, like a quarter of the screen.
The feature that really makes PowerResizer stand out, however, is dynamic resizing. Once you’ve placed your program windows where you want them, rather than docking and resizing all of them again to change one of them, you can simply start reshaping it and all the others will automatically scale themselves to fit around the window you are resizing.
PowerResizer is freeware, Windows only.