It seems a city called Centralia located in Pennsylvania was destroyed over the years from a fire beneath it.  Seems to me though, it would be a great place to put in power generators and use that heat since it just continues to burn.

When I first heard about this, I thought someone had to be joking, but it is a true story.  More can be found:

http://en.wikipedia.org/wiki/Centralia%2C_Pennsylvania

If the light bulb hanging in this fire station could talk, boy the stories it could tell over its 105 year life span, yep it has burned now for over 105 years.  They even have a webcam for it so you can make sure it does not go out without knowing about it :)

http://www.centennialbulb.org