Parallax is a really cool, powerful use of javascript from Stephen Band. Think of looking through a camera and having layers of objects at various distances moving around. Parallax achieves that effect using a combination static images, one for each layer.

“Parallax [is a jQuery library that] turns a selected element into a ‘window’, or viewport, and all its children into absolutely positioned layers that can be seen through the viewport. These layers move in response to the mouse, and, depending on their dimensions (and options for layer initialisation), they move by different amounts, in a parallaxy kind of way.”