I've always found it a bit annoying that you have to access screen preferences to adjust the brightness settings on Macs.
I know you can control it from the keyboard but since volume control is available from the Menu Bar, why not brightness? That's exactly what Brightness does, adding a discreet volume style slider to your Menu Bar so that you can control screen brightness more easily. Even better, PowerBook, MacBook and MacBook Pro users with a backlit keyboard enjoy a second menu bar item for adjusting keyboard brightness.
To install Brightness, open up the System Preferences, click on 'Accounts', 'Login Options', and choose the 'Login Items' tab, then add Brightness to the list. The only way to quit it is to open Activity Monitor to end the process, which is a bit annoying but once installed, you probably won't want to remove it anyway.
Brightness adds a much needed screen brightness controller to your menu bar so that you never need use your keyboard or access it through system preferences again.