I have funded these games so far
Castle story -- A voxel based strategy game which I belive is in alpha right now
Limit theory A proceduraly generated space RPG with an infinite world.
AGK -- AppGameKit, you should know what that is.
Both of the games had someting interesting and unique that I wanted to see done wich was what got me interested in them. They also had prototypes to show off which showed both the competense of the developer and that the project was actually serious and was able to do something without the money. Having something working to show off is the most important thing for me when looking at a kickstarter (atleast for agame) since it proves that the developers are serious about it and are able to pull something off. A few pieces of concept art and an idea isn't going to make me back a project.
Both castle story and limit theory are made by 2 previously unknown "teams" LT only has a single developer, but the point being that you absolutley don't have to be famous to succed with a kickstarter, you just have to have a good idea and prototype and show it off in a good way.
As for rewards for games, like quick said, getting access to early versions of the game is always appealing and will make a lot of people throw more money at it. "Selling" the game at a discount from the final price is also a good idea to bring more backers. I also enjoy having soundtracks for my games so offering that as a reward could be a good idea. Overall, I feel that physical rewards are mostly just a pain for both you as a developer and for backers, but giving some people a map of the world for your game as a higher tier might not be a bad idea. Just don't focus to much on the rewards, if have a product that has a lot of potential, people will want to support you, even if the rewards aren't the best.
EDIT:
Looks like some posts slipped in while I was writing this
Quote: "and, honestly - as long as you can show that you got something going - and are not just presenting an IDEA"
Unless the developers can show that they can pull something off, I won't back them. Having a lot of experience or showing something actually working are both ways to do so. Kickstarter is already pretty crowded with idea state game projects which hides the ones that actually have something going.
Say ONE stupid thing and it ends up as a forum signature forever. - Neuro Fuzzy