I have, what I think is a great idea for a Star Wars novel. They only problem with that is that you can't just write a Star Wars novel. If I wanted to pursue this idea seriously, I would have to draw up an entire outline for the book, write the first few chapters, and then wave some kind of magic wand to land an agent who could present the idea and hopefully sell it for me.
I'm not sure if it would really be worth it, but unfortunately, the idea just won't leave me alone...