If you are looking for something that you can bring with you in a backpack and don't want to worry about it catching on fire the Coghlan's Fire Sticks work very well. You can light them even if they get wet so rain is no problem. If you don't care about portability or stability you could use newspaper and lighter fluid. you can get all kinds of camping and fire starting accessories at www.poorfish.com

I'll second the cotton balls with Vasoline, but I'll also add jute twine. You can cut small sections and fray it to make excellent tinder. And when you're not burning it, you can tie stuff with it!

if you're looking for something that's in the woods, birchbark is my favorite, if you get the fine stuff, it will catch a spark, and the bigger strips burn amazingly bright. as far as vasoline on cotton balls, that does work great, but if you want something less messy that will burn better, pack a small bottle of rubbing alcohol, it will clean out wounds, but if you soak a cotton ball in it, it will burn for around 4 min with a 10" tall flame, compared to an average of 3 min and a 4" flame for vaseline cottonballs. also it burns more cleanly than vaseline or petroleum.