BetterTouchTool

http://www.bettertouchtool.net/

BetterTouchTool is a great, feature packed app that allows you to configure many gestures for your Magic Mouse, Macbook Trackpad and Magic Trackpad and also Mouse Gestures for normal mice. It also allows you to configure actions for keyboard shortcuts, normal mice buttons and the Apple Remote. In addition to this it has an iOS companion App (BTT Remote) which can also be configured to control your Mac the way you want.