This has quite a bit of adjustability and reach for a bar end. I've used it on pull backs and drop bars as well as flat and MTB style.
http://www.bikestoreguys.com/product...Bar_End_Mirror

Stay away from the inexpensive old school style bicycle specific chrome mirrors. The clamping mechanism is cheesy (a flimsy piece of strip steel) and the ball joint at the back of the mirror is usually cheap and has too much play in it. If you want the old school look then get a version intended for motorcycle use because they are much more robust with a decent handlebar clamp.