YA/fantasy writer Justine Larbalestier has deemed January to be Writing Advice month in her fabulous blog. Take a look if you're in need of writing advice of any stripe.
I'm only up to the "How to Get Unstuck" post, but so far it's all so right on the money.
My own thought on how to get unstuck when you're plot seems dead comes from screenwriting. Take a break, then come back and write down any and all thoughts for scenes for your book/story on separate notecards. As Justine says - have two characters that don't meet in the story meet somehow, throw in some explosions, whatever. It's all allowed. You'll be amazed at how this starts to trigger other, more logical ideas for scenes or connections in your story. Try to figure out how to get from the scene on Card Y to the scene on Card Z. This will lead to a flurry of other ideas. Not all the cards and ideas will be appropriate for your story in the end, but I bet you some of them will be great.