myLED Torch app for iPhone and iPad
This application allows you to use your iPhone 4 as a torch / flashlight.
It will use the LED flash as a flash light, but you can also configure it as a strobe light too. You can change the speed of the strobe light as well.
Finally you can also choose to make the entire screen of your iPhone white too for that extra bit of light.
Disclaimer: Continued use of the flash may dramatically decrease battery life.