I'm opening up this topic just as a place for discussion and link-sharing. We already have a bunch of instructables on hydroponics and small-garden farming. Let's see what else people come up with. Urban agriculture is a much less energy-intensive way of producing food, mainly because the product is transported very short distances to its consumers.
Here, for example, is a Saskatchewan business that is promoting ways of doing urban agriculture as a profitable business:http://www.worldchanging.com/archives/006935.html