There are two categories of tinder: tinder that will catch with a spark, and tinder that requires a standing flame. For purposes of this article, I'm limiting myself to tinders that are readily available and either phenomenally cheap or free. (Most of them were sourced as "Things found in my wife's car or purse.")
Standing Flame Tinders
Paper: Receipts, business cards, note paper, even checks if you're desperate. Crumple it up loosely, touch a match or lighter to it, and you're on your way.
Styrofoam: Sourced from drinking cups and takeout food containers, foam burns hot and easy and is waterproof. Break it up into palm-sized chunks for easy starting. Be aware, Styrofoam gives off some nasty fumes when it burns, so don't use it in an enclosed or poorly ventilated area.
Dried grass: A fluffed-up ball of dried grass is a classic fire starter. Look for grasses that have turned to yellow or brown. If it's warm and sunny during the daytime, standing green grass can be cut and dried easily.
Dryer lint: Lint is almost weightless, and the price is right. Fluff up a bit of lint into a loose, fist-sized ball and it will catch readily and burn hot and long.
Jute twine: As mentioned in the fire bag article, I carry a fair bit of jute with me. It is one of the easiest-lighting tinders I've encountered. To use it as tinder, snip off a few inches, separate the strands, and fluff them. You can even buy 520 foot spools of it on Amazon, if you can't find a better price locally.
Cotton balls/pads: Use the same technique as with lint. Some people impregnate them with petroleum jelly to make them waterproof. For cotton make-up pads, peel them open to expose the fluffy center for the best results.
Practice up and go start something.