Coders Block (Score 1)

I find juggling to be a great help... it takes your mind off the problem, and gets both halves of the brain working again. Some of our developers at work have setup a fish tank and a large punching bag to help with their stress/blocks. Still, there is no substitute for fresh air and sunshine.. going for a walk, swim bike ride etc doesn't just improve your physical fitness. As someone else stated, flicking through a couple programming books (even on just the basics that you are sure you already know) can also help.