I really like a firesteel + trioxane. Fastest, easiest, simplest, most reliable method I've used.
I carry a lighter or two, sometimes matches, but the firesteel works no matter what.
I think the Wetfire stuff that mtwarden mentioned is the same as the military's replacement for trioxane(not sure on that one). I don't know how easily it lights, or how long it burns, but from what I've read it works in about all conditions.
Vaseline/cotton balls-works pretty good, but you have to make them, store them, etc.
Dryer lint-depending on the content, takes a spark easily, and burns well. Doesn't burn that long, or necessarily that hot, but I've taken a bag of it with me a bunch of times. I have plenty of trioxane, but the dryer lint is free, so might as well use it...
I do stick mostly with the trioxane, though. If I can boil a cup of water over the tab, I can sure start a fire with it under most conditions. Started my last three campfires with three pieces of the same trioxane tab, and three strikes of the firesteel.