A quicker page down and page up.
This is especially faster on portables and the new wireless iMac keyboard where you have to press “Function – down arrow” or “Function – up arrow” as a page down/page up. It works in a lot of applications, as long as you are not currently in a text box (it doesn’t work in Pages for that reason).
It works in Mail, Safari, Firefox. To go down, you can simply hit “Space Bar” and you can go up with “Shift – Space Bar”. It works very well and it is, nearly all the time, so much faster. I actually use it on my full size keyboard.