MagicPrefs
http://magicprefs.com/

MagicMouse multitouch tweak. Includes MagicMenu, a 4-way multitouch popup menu.

free magic mouse preference panel that reveals hidden functions for the magic mouse

Adds middle-click to the Magic Mouse plus other great swipe functions.

MagicPrefs is a free menubar and preference pane application for OSX which aims to improve the functionality and configuration options of the Apple Magic Mouse. It features the ability to bind a variable number of finger clicks, taps, swipes, pinch and other gestures to functions like Middle Click , Hold Down Both Mouse Buttons , Spaces , Expose, Dashboard etc.