The California hands-free calling law goes into effect on July 1, 2008, which bans cell phone use while driving. However, hands-free devices such as Bluetooth headsets will still be legal. Here's a list of our favorites; hopefully one of them will be yours, too.
The Aliph Jawbone is a premium Bluetooth headset with amazing sound quality. Beware its quirky fit and controls though.
If you like the idea of a Bluetooth headset but dislike having to wear one, the Cardo S640 might be a good compromise. You can clip the unit to your shirt, and then only wear the ear bud when there's a call. The ear bud tucks away neatly in the device when not in use.