I used the Blackburn Road Mirror on my old bike. It Velcros onto the brake hoods on any bike with drop bars. I could see behind me with no problem, even when stuff was piled on top of my panniers.

http://www.blackburndesign.com/mirrors.html

The brake hoods on my new bike are beefier than those on my old, and I did not like the bulk of the Blackburn. I switched to a Cat Eye that mounts in the bar end. Visibility is not quite as good as the mirror mounted on the brake hood -- my arm often gets in the way -- but it's OK.

Alan