Moom allows you to easily move and zoom windows to predefined areas of the screen, or to make them full-screen, using either the mouse or the keyboard.
When used via the mouse, all you need to do is hover over the green resize button in any Mac OS X window. Moom's panel appears, and you then click the desired action.
When used via the keyboard, a hot key displays the Moom bezel, and you can then use the arrow and modifier keys to move and resize the windows.
You can also save window layouts, create custom controls with shortcuts that work globally or work only when Moom's keyboard bezel is onscreen.