I use a Take-a-look myself. They make a small one for eyeglass mounting and one with a larger mirror and longer "boom" for helmet mounting. I've used both but usually prefer the eyeglass one, as it vibrates less and seems to give me a better field of view. They can be a pain to adjust though.

I tried a Blackburn bar-end but didn't like it. It vibrated way too much, plus if you have to lay your bike down on the left side (which you're supposed to do to protect the rd hanger and keep the drivetrain out of the dirt), it can knock the mirror out of whack.