- A plot doesn't have to be new. It just has to be new to the reader.
- In fact, it doesn't even have to be new to the reader. It just has to get past him. (It helps if the story's moving fast and there's lots of other interesting stuff going on.)"
Full essay -- with random number generation! -- here.
Still, even if you don't get inspired, the proposed ideas can be a lot of fun to see together.