THE KICHI GUY  one of the essential freeware/shareware apps for the mac. highly customizable, works in every app (not just cocoa apps), and with a little bit of creativity, you can practically control any aspect of your computer with this.

and blackflag, it is easily worth your $5 burger king lunch. and don't be disappointed, xgestures can easily handle the one thing you wanted it to do. just add the finder to your app-specific settings, choose the gesture action "Choose Menu Item", and for the menu item name type "Back" for going back, and "Forward" for going forward, and then assign whatever gestures you want to those functions.  
(Version 1.7)