In my day job I'm responsible for the exterior lighting for a British motor car manufacturer. In new headlamp designs, control of condensation is a major concern. Applying much the same principles to a bathroom mirror:

Misting of mirror is caused by combination of three things.
1) High absolute humidity of air in bathroom.
2) Temperature difference between warm humid air and colder mirror surface.
3) Angle of contact between water droplets and mirror surface (related to surface tension) such that droplets can hang on a vertical surface, diffusing the reflected light.

To address 1) only option is extraction/ventilation: replace moist air with dry air.
To address 2), keep the mirror warm. Don't put it on an outside wall. If you can, put it above a radiator or in the airflow from fan heater. On the other hand, infra-red heaters are good for keeping you warm, but useless on mirrors which reflect rather than absorb light, visible or otherwise.
To address 3) most of the materials suggested already will work either by letting the water flow out into a film which doesn't break up the light the same way, or better by making the droplets near spherical, which will run down off the surface under gravity.

In UK, Pilkington sells "self-cleaning" window glass, which works on the last principle. Maybe they should also market it for bathroom mirrors.

nick