This article is from the Toyota Tundra FAQ, by Steve Yee with numerous contributions by others.
Some dealers will install an optional Compass Mirror, which shows direction and
heading of your vehicle as you drive. Currently, there are two manufacturers
of this type of mirror. One version of this mirror can be purchased directly
from Donnelly Electronics Corporation for around $215. Donnelly's link for the
Tundra specific mirror can be reached at
http://www.donnellye.com/_private/prod01.htm. Gentex also produces versions of
these mirrors and are OEM mirrors for some other car manufacturers (such as
GM). Gentex's web site is at www.gentex.com. You can purchase a Gentex mirror
from Mito Corporation at www.mitocorp.com.