You can't sell an idea because you don't own the idea. Try this link for a seven-minute web video interview on exactly that question. And this one for a four-minute link.
And I don't mean that you didn't think it up. I mean simply that the only legal ownership is an invention, for which you'd need a patent, and patents are expensive, take a long time and don't really guarantee protection.
Companies don't even want to talk to you about your idea, because for all they know, you've thought of something they're already working on, and if they talk to you about it, you'll be able to say they stole your idea.
The way real people with real ideas get value from them is by building a company to implement those ideas. Then you can own it because you own the market, you were first, you're branded, and everybody else is just imitating you.
Question added to topic Franchises • November 4, 2008
How do I sell an idea for a product?
I have a great idea for a product to help parents with potty training toddlers. Do I approach a company that would manufacture the product to see if they would want to buy the idea, or do I come up with a prototype, trademark it and then try to sell it? I would prefer to just sell the idea. I have asked many parents of toddlers if they would buy the product and all agreed that not only would they buy it, but would pay a lot for it.