What are your favorite resources (educational or entertainment) on YouTube?

We have especially enjoyed the Eureka series of science videos (my kids incline in that direction): and from there they are linked one to the other. There are thirty-some episodes.

I would love it if others would share their favorites.

DeeDee

Minutephysics is a current favorite.
Khan academy science videos. The ipad app now lets you download videos so you can watch online.