Bio2imaging has Heart Beat Rate Pro (iTunes Link) for the iPhone and iPod Touch in the iTunes App Store for FREE (regularly $1.99) for a limited time.

The Heart Beat Rate app uses your smartphone camera as a heart rate monitor.

Thanks to an innovative image analysis process which tracks your blood flow in real-time, it gives a direct and reliable measurement of your heart rate.

All you have to do is cover the whole camera lens with your index tip, and the application will compute your heart rate in real-time while displaying the pulse signal in a graph.