If you don't shave in the shower, you should. And if you shave in the shower, you need the Shave Well Fog Free Mirror. Seriously, just buy one.
I've tried countless shaving mirrors over the year. This one wins hands-down, and it's great for traveling too. It's plastic so it won't break, and light enough that it won't weigh you down.
Some "fog free" mirrors use special coatings or complicated water-circulating attachments to keep the mirror clear. I've tried all those. They suck. The Shave Well uses science--you lift the mirror from its hook and run it under the water for a moment. This equalizes the mirror's temperature with the water's so it doesn't fog up. Simple. At only $10 this one is also less expensive than most other mirrors.
The only improvement I'd make to the Shave Well mirror is that it comes with a hook that has permanent adhesive. I don't want to stick that to my shower wall, and I want to travel with the mirror, so I bought a package of inexpensive suction cup hooks at the grocery story and threw away the hook they supplied.