I’m using a Jawbone 2 now. I’ve had it for a couple weeks, and it’s working great. Good sound quality on both sides, works fine outside and in the car. (If you’re buying from Amazon, don’t buy the bulk package version. According to the reviews, it doesn’t come with all the right extra bits.) And make sure you’re getting a version 2, not the original Jawbone – the original is terrible.
The previous headset I tried was a Plantronics Discovery 925. Indoors, it was fine. Outdoors, it was useless. A slight breeze and the person I was calling said it sounded like I was in a hurricane.