I started with the biggest, ugliest, priciest, helmet mirror possible, the Safety Zone:
http://www.amazon.com/Safe-Zone-Bicy...401722&sr=8-14
I have also tried the Take a Look eyeglass mirror. The Safety Zone is head and shoulders better than the eyeglass mirror. However, it does take a while to get used to it being there. You feel like the Borg wearing the thing.
On my hybrid I have a handlebar mirror and absolutely love it; much nicer than the helmet mirror or eyeglass mirror. I like it so much that I am looking at handlebar options for my Madone.
Here is a review of two options for bar end mirrors for drop bars:
http://www.signatureride.com/PRtwomirrors.html