I found this on Kickstarter:
"FLASHr is an iPhone4/4s case that is powered by the iPhone's LED camera flash, and iOS's built in "LED Flash Alerts". When you turn on "LED Flash Alerts" in your Accessibility settings, your iPhone's LED camera flash lights up for calls, texts, emails, and for all Push Notifications (Twitter, Facebook, Games, or any app with Push Notification settings)."
It's pretty neat for anyone who wants a silent notification that's still very obvious. You can get one for a $35 USD pledge on Kickstarter.