Just got myself a Jawbone Up24 as a bit of an experiment. Sunk £125 on it, but it seems pretty cool so far. I think you're mainly paying for the application rather than the wristband itself as the app requires it.

Just to cover what it is, its a wristband you wear that tracks your steps, pace, exercise routines, sleeping habits, sleep quality, and calorie intake. Gives you fitness tips and shit.

I'd recommend it if you have bit of spare dough, the battery life is about a week and it syncs with your phone via bluetooth (I think you can get a sans bluetooth version for a bit less).