If you are into size as a factor I use this it works great and it fits very well. This is probably the smallest your are going to find. Of course if you have more than 1 bluetooth phone you may want to consider this one, supports pairing to up 8 phones. But it is pricey.
I just got the Plantronics H640 three days ago. It's great. If you want to know what's what about bluetooth go to Bar John Reviews. Link There you got it all.