Something else that I have built is a Rocket stove. They are easy to make and quite efficient. The big advantage to them is that they will burn twigs, dried brush, and other small debris that you normally would not use for fuel. If you are faced with a shortage of fuel, this would be a great stove to own.
I made mine out of a five-gallon can and some scrap 4-inch pipe and a old piece of grill. It works very well. You get a surprising amount of heat out of small twigs and branches. You can make stoves from almost any size of a can and old pipe. I have seen pictures of large ones made of brick. One of these days I will build a brick one in the back yard.