I have a Nike + iPod Sport Kit that I won. It is no use whatsoever to me (those who know me will understand why). I'm guessing it can be used in any make of trainers but it's advertised in conjunction with Nike.
It is stil in the box and unused If you're not sure what it is, then this
They range in price from £15-£18.99 retail, but it's yours for £10 (the cost of the prize entry I won it in). Ideal gift for the fitness freak in your life