Pace.fm is a distraction-free way to keep track ofyour current pace, while running, walking, or cycling. Pace.fm willincrease or decrease the tempo of your music, relative to your currentspeed.
I've had this idea bouncing around in my head for quite a while now. Finally got around to putting together a prototype over the past couple of weekends and it works really well. Sign up to be notified when it hits the store.