I'll also vote for heart-pine kindling wood (or fat-wood) as the others called it...
For those who haven't tried it -- you really should. Next time you're in the woods and see some pine knots lying on the ground from where a pine (yellow, jack, loblolly, or red pine are much better than white pine) tree has rotted away, pick a couple of them up and take them home. The heavier the they are, the better they are -- because that means they're full of pine resin (pine tar). Use a hatchet or very sharp ax and split them into very small slivers (between the size of a match-stem and a pencil) and try it. They'll burn higher than the match you lit them with, give off a wonderful smell, and a small handful of kindling will start a fire with about any dry wood. If they don't want to light directly, take your pocketknife and curl up a shaving or two to start.
Good, rich pine knots will burn like paraffin and smell much better. Plus, they're absolutely free. Try it, I think you'll like it...