$1: Standard muchas gracias
$5: Your name is added as a random sentient historical figure at the beginning of worldgen. You have a chance to see engravings of yourself being eaten by a dragon, or becoming lord of an empire.
$25: Crayon picture (probably a copy)
$50: DF Shirt or hat
$75: Signed DF poster
$100: Your name gets added to a list, from which the names of Fluffy Wamblers will be chosen. All Fluffy Wamblers will have a name, drawn from this list. Special thanks mention. Limit 500
$250: Towns in worldgen can be named in your honor, civ of your choosing. Limit 50
$500: New animal you get to describe and name. Subject to approval, obviously. Limit 25
$1000: A new "vein" stone is named after you, color and properties of your choosing. Limit 10
I'd be careful with the really labor-intensive stuff, especially at low levels. Even a short story and signed crayon picture takes time to write, and if they've got to do a THOUSAND of them we'll never see DF released. Even simple signed stuff can take entire days if you've got to sign a lot of things. Judging from some of the recent Kickstarter success stories (there's a game that got 11,400% that I'm looking at right now. No typo), the response to DF would be huge, especially with the huge swell of recognition it's starting to get. Even for shirts and hats, Toady'd have to hire people just to co-ordinate the logistics of ordering and shipping them.
Don't think Toady will go Kickstarter, though. Seems like he wants to do all the coding himself and make sure his baby turns out exactly the way he wants it. Sure, it'd go faster if he got a million dollars from Kickstarter and hired a whole team, but I think it'll turn out better his way. We just have to be patient =p