I will never understand why you would have a runner's watch and an mp3 player. Just strap on your smart phone and you are set! Friends always tell me it seems like your smartphone is too big to run with, but it really isn't. Aside from tracking my workout and playing music, I have my phone in case of emergency.
For awhile I was just using CardioTrainer until RunKeeper got it's act together with Android, but by the time that happened I was already hooked on CardioTrainer. I use the Free version of CardioTrainer and it has more features than RunKeeper Pro ever did. I love that I can look back over my history and track my workouts, pace and miles. It really helped motivate me and one up myself.
If you are a runner, even a beginner, I encourage you get this app and start tracking!