Warp is a preference pane that allows you to use the mouse to switch between Spaces rather than using the keyboard. Warp offers the ability to display a live preview of a space when you move the mouse to the edge of the screen, allowing you to see what you have on another space before actually switching to it. Clicking the preview will then warp you to that space. (Enable this feature by checking the option "Click screen edge to Warp" in Warp's preference pane)

Requirements:
OS X 10.5-10.6
Universal Binary