+1 on the Take-A-Look mirror. I had a helmet mounted model before, and the optical quality of the mirror had much to be desired -- also the placement seemed to cause a good deal of eye strain. What finally killed it is that the helmet mounted one got knocked off and the adhesive would not work anymore.

The Take-A-Look works fabulously without the eyestrain of the helmet mount and it slides on my glasses easily. It has gotten to the point where I don't like to ride without it -- it saves me daily from roadies training on the MUP who don't call out when they are going to pass, even if it is obvious that I'm passing a pedestrian ...