[MetroMPG]

From the Chalmers University site:

According the the following article, the rear view mirrors contribute 3% to 6% of the total vehicle drag.

http://www.tfd.chalmers.se/~lelo/rvad/reports/rva2002_gr11_contribution-to-drag.pdf

The following article also has a lot of basic information about drag reduction in cars.

http://www.tfd.chalmers.se/~lelo/rvad/reports/rva2002_gr10_drag-reducing.pdf

EDIT:

.03-.06, is 3-6% of total drag.