I second Mcavana on the helmet mirror. People may laugh, but it is easy to align the way you want it, and you can tilt your head to see almost anything behind you. After a short while it becomes second nature.
I've had handlebar mounted mirrors, they tend to vibrate out of position, often steal a hand position from me, and cannot be adjusted on the fly like helmet mirrors.
For those with vision trouble they can be mounted on the right side and used to scan traffic just fine. I did a tour of Ireland, riding on the left side of the road with my mirror mounted on the left side of my helmet, and still was able to use my mirror without difficulty. So it should work vice versa.
Helmet mirrors DO create a blind spot in the forward view, and one has to get used to moving one's head a bit to make up for this. Bothers me less than having to constantly adjust a handlebar mirror.