Here is an app that falls under the category of i didn't know a phone could do that. It uses the camera and an LED light to read your heart rate. It is a nifty trick if nothing else.
https://market.android.com/details?...m1vZHVsYS5hbmRyb2lkLmluc3RhbnRoZWFydHJhdGUiXQ..
https://market.android.com/details?...m1vZHVsYS5hbmRyb2lkLmluc3RhbnRoZWFydHJhdGUiXQ..