quicksilver is a pretty nice app and free. basically, instead of clicking on an icon in the dock or navigating to it with finder, you hit a couple of specific keystrokes to activate quicksilver and then start typing the name of the app or file you want to launch.
for example. to start up safari, i hit ctrl+space to activate qs. then i start typing s-a-f-a.... by the time i get to 'f' it has found safari and i hit enter to launch. much easier for me than going through finder, or grabbing the mouse all the time.
it also allows you to install plugins to do various other things like define words, send email to specific people, and use it as a calculator.