You must have heard of the Million Dollar Home Page by now. A 21 year old English guy had an awesome idea to create a medium that is a venue in itself. He's simply selling space on a web page 1$/pixel as advertising space. He has got 1 million pixels to sell, therefore he is planning to make 1 million dollars of advertising money on his webpage. The novelty of the idea draws traffic. And, like an accident on the road - traffic drives more traffic. And, where there is traffic - advertising space can be sold. It's a self fulfilling prophecy.
If you were wondering if he can make it, well he already sold 4% of the space, which made him 40 thousand american dollars. His site made into several blogs and even C|net. As the ultimate sign of success - he got a copycats: The Zero Dollar Homepage, Twenty Thousand Dollar Homepage, The Million Dollar Web, Million Euro Homepage, One Million Pixels and Million Penny Homepage. The ball is rolling and money is flowing.
Moral of the story. You can indeed make one million dollars with a 500 USD investment in the advertising business. All you need is a BIG IDEA!