It seems like there are two types of crowd-funding projects: charity and seed funding.
The charity type is pretty obvious. People ask for money for various reasons (medical bills, honeymoons, pool streams, etc.) and in return donors get to feel good about themselves.
What I have seen with seed funding efforts, is that a company (could be one guy) needs initial investment to get an initial run of a product made. They offer tiers of support (money given) with different benefits.
I recently funded a kickstarter program for a new board game. In exchange for the money, I get a copy of the game and few bonus bits that won't be available to "regular" customers. If I gave them more money, I would have gotten more bits. One funding level even got you dinner with the creator and a night of playing games with him. (if you like board games, that's a really cool deal.)
So basically, if you want people to fund your business, the question is what do they get in return?