If you’re in a writing mood, plotstorming.com does a lot to help you out. The daily writing prompt is pretty neat– just enough to spark a short story or two, if you’re in the mood. (I found this site via a post on the Treasure Tables forums, and found that it’s a nice little place.)
They also have an area where you can work on a world– for a book, RPG, or whatever you need.
A similar site with more of an RPG focus is The Campaign Builder’s Guild. Their Homebrew Campaign Settings page has an impressive list of worlds you can borrow.