+1 on CycleAware if you're going for the handlebar mount.

I personally wear my mirror clipped to my glasses... I like and currently use the "Take-A-Look" and like it because of light weight, ease to clip on and off, and the nice wide field of view that it gives you. CycleAware has a similar version with a plastic frame, where the long axis of the mirror is vertical rather than horizontal like the Take-A-Look. I'll probably give that one a try ths summer sometime.

They also have this absolutely cool "Torpedo" insulated water bottle as a new product... They had a bunch of them at the Smart Cycling conference in San Jose this past weekend, and these things will ignite Water Bottle Envy in anyone...