FitBit?
I don't have a fitbit, but I do have a Polar Heart Rate Monitor watch which can be cheaper if you are just looking to count the calories that you've burnt! If you shop around these can be cheaper, but you also have to wear a strap around your chest so the fitbits tend to be more convenient.
I've just ordered a Fitbit Charge HR. I'll let you know how it works out.
