I’ve got two applications for bike riding on my iPhone:
One is called GPS lite by Motion X. It works great, but is really kind of beta; it only allows for three points of interest to be saved. This version is free, but they say that the full (paid) version is coming shortly. I can’t imaging mounting this on my handlebars, but I use it to record my rides and look at how far Iv’e ridden. The battery life is pretty limited. If the ride lasts any longer than two hours, you had better have a charger handy when you get to the car. When I ride with it, I start logging, then pack my iPhone in my hydration pack and start pedaling. It’s pretty well protected that way; I’m not all that worried about damaging it.
Just last night I downloaded another one called Trails. It records your ride or hike, and it will display it on a map, and you can also export a .gpx file to share with others. You can download files from a few selected sites as well. I only used it to record my .37 mile walk to the gym, so I can’t really speak about how well it’s going to work.