Set a timer for ten minutes. Close down your Internet tabs-- all of them. No Twitter, no Facebook, no Pandora, no nothing. NO CHEATING. Open a new document. Do not open any saved documents. Stare at the blank screen until the timer goes off. Do not force yourself to think about anything specifically. Just sit.
Now write about wherever your mind had wandered in those ten minutes of pure freedom.
If it was not directly related to one of your works in progress (for example, all you could think about was your dirty dishes piling up), then find a way to make it related to one of your works in progress.
Like... wouldn't it be great if those dishes could wash themselves?
Voila! "Dirty dishes" meets Arthurian fantasy.