I really like my Safe Zone mirror. It's durable, stays where you put it and has a nice big mirror giving me a great field of view. You are going to get a lot of replies of fans of the other more popular mirrors, those are definitely smaller and more minimalistic if you prefer that. I can't foresee needing it, but it's also got a 5 year no-fault warranty. Also, although I doubt it's an advantage against most of the other popular smaller mirrors because I think they are made here to, but it's made in the U.S. if that matters to you.

http://www.amazon.com/Safe-Zone-Bicy.../dp/B003LVHZ4O


Here's another one I don't see mentioned in these threads:
http://www.bottlecapbikemirror.com/B...e-Mirrors.html
I haven't used the Bottle Cap Mirror but I can see where it'd appeal to some folks too.