The Plantronics 925 is my choice for bluetooth headset. There are several very good high end alternatives like the Aliph and Blueant, but the 925 has the best combination of appearance, price, battery life, noise cancellation and size. Does voice dial for most devices, too.It really shines with a very cheap, easy mod. Add an Etymotic windscreen for $1.75 and it's just about as good as you can get.
Here's the best price I could find for the 925. Here's the windscreen source. Less than $80 for a real killer combo!