Juggling was recommended to me by a physio because I was getting shooting pains in my wrists. I used this to learn:

http://video.google.com/videoplay?docid=-6366713757585864298...

I find it rather good for thinking about bugs, as it's totally automatic once you get the hang of it.

Learning new things (mills mess at the moment) is great for coding productivity too. I can only handle dropping things every 10 seconds for about five minutes before giving up on procrastination and getting back to work.