The RoboStrobe app is a strobe light app that you uses your iPhones flash function. When the app is used it casuses your iPhones flash to pulsate matching the music that is being played near it. Ive actually tried this app and out and it works pretty good. I would also say that having a clear case on your iPhone gives you a better effect than without but overall this app works.
The RoboStrobe app is available for free in the app store
Check out this cool video of the RoboStrobe app in action: