There were some links on MetaFilter recently that might be useful for physics lessons.

Flash Animations for Physics. “Animations and interactive demos available in many varieties, such as classical mechanics, nuclear, quantum, and relativistic. There’s even a nice explanation of the forces at work in Curling. And if that doesn’t wet your geek whistle, then take a peek at the patterns of Visual Math.”

Stellarium. “A free program which renders realistic skies in real time, and more. Handy for anyone who ever wrangled with one of these. And very cool to watch in fast forward.”