Essential Mac OS X tools: Scroll Reverser

Scroll Reverser is a free app for Mac OS X that reverses the direction of scrolling. You can use it with OS X Tiger, Leopard and Snow Leopard to make your scrolling match the ‘natural scrolling’ in Lion.

via Scroll Reverser for Mac OS X.

I use it on Mac OS X Lion in order to use natural scrolling with the trackpad of my MacBook Air and unnatural scrolling with the attached mouse.

(kudos to @romeroabelleira for the hint)