I use a Polar S625x, it is a bit pricey but it is well worth the money, it comes with a receiver (watch) foot pod that attached to your laces and a heart rate monitor which is a strap that wraps around your chest. From the research I did the nike plus system can be off up to 10% before you calibrate it the polar system is 97-98% accurate out of the box. The nike plus system can only be uploaded online, polar has exersize software that can be stored either online on local on your pc and you can set schedules etc. It doesnt use GPS so you don't have to worry about losing signal and if you don't have an ipod nano you dont have to go out and buy one, the foot pod sensor is built that it fits into any set of laces, it also has other stuff on it like an altimeter and temperature readings, if you dont have an ipod than you might want to consider the s625x, it doesnt use GPS which can be good (doesnt lose signal) or bad (if you like knowing your coordinates), you can also buy a seperate bike sensor which tracks your speed, cadence, distance etc. I have one and I am very please with it. If I had already owned an ipod nano tho I'm not sure if I would have gone out and bought it if I was just looking for a speed/distance monitor.