I used to be a HUGE Nike+ fan and I still think it is awesome. But I find myself using the run keeper app more now. I like I don't have to clip anything to show, or calibrate the little piece. Run Keeper (does more activities then running) just using GPS and maps your route and calculates how far you went, how fast, incline, how many calories. You have an account online very similar to Nike+.
Anyway, it is all FREE. Assuming you have a device that can use the app. You have to pay for Nike+ and if the battery in your little shoe pieces dies, you are SOL and have to get a new one. You also have to clip the thing into your ipod or whatever. I always have my phone on me, so I am ready to track my walks whenever and wherever I am! Does use a bit of battery though.
http://runkeeper.com/running-app