This is kinda neat. I did not try ‘TestRides‘ (by Wildlab) myself, but I like the idea. Basically, you take a picture of yourself, select key body points to provide an overall measurement set, and then calculate and display the best bike size for your body. Sweet! For people who do not do a lot of biking, having the wrong size bicycle is the difference between have a pleasant long ride and one wishing it would end. The app just came out, and looks a bit early in dev, but if you have never been fitted for a bike before, I think it's worth the $5 to find out. Who knows? If you had the proper bike, you could be riding twice and far with 1/2 the pain.
Also, if you did not already know, but you can use your iphone as a biking computer.