I have no idea where this should go (I know, I should know since I’ve been a member since 2002 and I obviously spend a lot of time here) so I have no problem with it being moved.
I am partial to computer based things that make good use of accurate physics. I know there are flash and java apps out there that demonstrate good physics.
If you know of any, please post links to them.
I think I got this link lurking the Dope years ago. You may have seen it already.
http://www.digipen.edu/main/Game_Downloads
TONS of student-made games. Some raw experiments, and some very polished games.
Jay Is Games is quite possibly the best place to go for online games:
Is the NLOS Cannon Challenge the sort of thing you are looking for, or are you after something a bit more grown-up than a reskinned version of Worms?
My husband likes this site.
I had a lot of fun with the West Point Bridge Design Contest in high school. I’m glad to see that it’s still around.
Aside from N (thanks, Agent Foxtrot!), Gish and Armadillo Run are two of my faves.
Oh, and Crayon Physics 
You may know about this one because there was a fairly extensive thread about it, but I’ve become addicted to Fantastic Contraption.
That was Contrary’s link and I am just addicted to it. I have no idea what the “right” solution is to most, but I always end up with jumbling piles of sticks that bounce all over the place until they finally reach the goal. Good fun.