Got an email from the webmaster of http://www.noggintwisters.com:
"Here's a new website full of math and science puzzles, problems and simulations, ideal to supplement traditional or home schooling education.
Hope you find a way to mention us."
Seems like there are some good puzzles there, so I have (mentioned them, that is).
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
Good website...and Einstein's problem is the hardest there according to them.