If you are going with that style mug contemplate one of these
http://www.thinkgeek.com/product/112...FYwDvAodTW4AvQ
http://www.thinkgeek.com/product/eb62/
it heats on 12v - not necessarily good from cold (unless you have hours!) but I had percolated coffee I bought at Port Augusta still hot (& I mean hot!)
as we got to Melbourne.. thats pretty good I reckon!
But, They usually are on or off, they don't regulate the heat.. I did have one with a digital temp etc setting on it but every time you stop the car it resets.. drove me mad on daily stuff!

