Requires iPhone4
FlashLock is a simple yet handy tweak that allows you to quickly activate the LED flash of your iPhone 4, right from a button in the Lockscreen slider bar, like the iOS 5 camera button. The whole concept of the tweak is an idea of Sebastien Page, who also came up with the name.
(Double tap the home button while in the lockscreen to make the button appear).
This tweak affects the lockscreen. No new icons are added to your homescreen. You can configure options from Settings.app.