I use mapmyfitness app on the iphone. Its fab but eats battery. Its easy to use, uploads a little map of your route and info to facebook or twitter (if you want to) and free

On the downside it seems to keep running but as soon as I get back to the car and press a button (as in save/end run) the phone dies. I dont lose the route or info so thats OK but it just meant I had buy an in car charger
Just to add it will tell you your current pace, speed, distance travelled, show you where you are and where you've been on a simple google map and I have mine set up to speak all this info to me every mile
http://www.mapmyfitness.com/
I have a personal GPS a garmin one - I cant use it properly only to back track the route Ive taken and can only upload a multi point route onto the program and then transfer to google maps and then have to use the distance measuring tool to check how far Ive been. Its generally pants (but does have geo caching on!)