EdgeCase: http://itunes.apple.com/us/app/edgecase/id513826860?ls=1&mt=12

I made this app to solve the biggest annoyance I have with using multiple monitors.

EdgeCase stops your mouse at the screen edge, even when you are using multiple monitors. When you do want to move between screens, you can do so by holding [ctrl] or [⌘], dwelling for 1/2 second, or 'bouncing' on the edge. In-depth description below...