App Switcher Brightness is a new jailbreak application - or rather a tweak - that adds a brightness slider to your iPhone app switcher. If you find yourself constantly changing the brightness of your iPhone screen, then App Switcher Brightness will most likely be a right fit for you.
Instead of having to go to Settings > Brightness, you can simply double press the home button to launch the app switcher, flick to the right to have your iPod controls appear, and your brightness control is there...