The Monty Hall Problem New York Times
Can't recall now where I first heard this, but it completely engrossed me at the time --and I am not much given to such puzzles. The challenge is one of those non-intuitive results that statistics gives us to a situation we all think to be perfectly obvious: Does it matter if you change your mind once Monty Hall opens a door on Lets Make a Deal?

Here, the times has turned the problem into a cool little animated interactive which lets you play for yourself.

Alas, it doesn't go the step further of doing an interactive with the math behind the problem.

PBS Impresses Me Steve Harrington
Lot of interesting stuff here on PBS' interactive efforts.

In fact, I labeled this post "Platforms" because that's what PBS is, isn't it?

International Music Score Project -IMSLP
Not sure how yo may use this on your projects, but an interesting open source resource all the same.