The best mirror I ever used was a crappy $3 department store one. Too bad I sold it no my Marin a few years ago figuring it would be easy and cheap to replace. I don't remembering it being to shakey, but that might have been becasue it was kinda flexible so maybe it absorbs the shakes and bumps. Anyway, what made it great was it stuck up higher into my field of vision and it was a bubble mirror so I could see almost everything behind me unlike some of these other mirrors I have seen and even my Blackburn bar end mirror that I think is ok isn't as good plus it sticks way out on the side of my bike which is annoying. The cheap one I had looked like these on ebay.
http://cgi.ebay.com/ws/eBayISAPI.dll...%3DI%26otn%3D2
I ordered 2 of these today for less than $4 just to see what they were like. They probably suck, but whatever for that price I can throw one on my mountain bike for when I ride through the neighborhoods to get to the trails. Worst case scenario they can be a sweetener of a bike I am selling. On the right bike a couple (ok maybe just one) mirrors in the moped style would actually look kinda cool.
I might have to check out a helmet mirror as has been suggested by a couple of posters. What ones do you guys have or suggest?