Here's a really cool application for the iPhone: Heart Monitor uses the iPhone microphone-especially the one built into your headphones-to record and track your heartbeat from your chest, wrist or neck. Watching the video, it looks like it will be a perfect application for both sports people and hypochondriacs, even while it comes with a couple of disclaimers:
Before buying Heart Monitor please make sure you can find your own pulse in your neck (directly below your jaw) or wrist, click arrows below the pictures for pulse locations. If you cannot find your pulse you may have difficultly using Heart Monitor.
If you cannot find your pulse, you may also be dead, but that's another story. It also says that the iPhone Heart Monitor shouldn't be used for medical applications, but it looks good enough for me. I'm planning to use it for resting, after going to the gym, and drinking five pints of Guinness while eating a greasy burger. OK, maybe just the first and third one there. The application looks like a winner for just $4.99. [Heart Monitor]