I used to use helmet mounted mirrors, but they look too dorky like you have an antenna on your head. I just switched to the glass mounted M2Racer Stealth Mirror and love it. The mirror is small in size, but since it is mounted so close to the glasses, the view is actually large and clear with little vibration. It is very light, compact and designed to be very stealthy, meaning that it is almost not noticible.
http://www.m2racer.com/products.php?...products&id=12