I purchased a rather inexpensive one at Walmart. I was surprised how many calories I burned by the end of the day. Moreover, I WANTED to walk more because the proof was in the numbers! So, ya get more motivated. I even walked during breaks at work.
It tells me how many calories I burned, steps I walked, how far I walked, etc. The brand I have is: GOWalking. Make sure you read the manual because you have to enter how big your steps are. I did not do this on my first day so it showed me that I burned a lot less calories than I actually did.