I've been using Cyclemeter on my iPhone. It's been a great little app and seems to be better then the others on battery life. It also has several biking modes, as well as running, swimming, walking, skiing, hiking and driving. All the data is kept on a web site and you can have each rides stats emailed to you when you save your data. I also have the pro version so everything is available to me.
One thing that I like about this app, that I didn't see in some of the others, is that all the data is present on the main screen by swiping left or right. It also pairs up with some of the popular HRM transmitters and cadence sensors.