Just picked up a BlueAnt Z9i
after researching dozens of headsets. This one got rave reviews for its sound quality, size, design, etc., but what really sold me on it is the ability to upgrade the firmware. Periodically, the vendor can release firmware updates to fix bugs, increase sound quality and so on. All you have to do is run the installer with your headset attached to your computer via USB and you now have the latest and greatest. I actually did this right after I got it, just to make sure I was up to date from the start.
So far the sound quality has been great, and the features are nice ans easy to use. I'm not big on headsets in general (I try to do as little talking on the phone as possible - send me an email instead 
), but for driving around town while on a never ending conference call this device is pretty cool.