Seconded.

Took me about 5 long videos and some Google searches to get into his frame of reference, but it was well worth it. The amount of useful ideas I got out of his talks is absolutely astounding. He really changed the way I think about programming, computing, user interfaces and complex system design.

I am slowly watching through all of the videos from Kay I can find.

A good compilation to start with: http://vpri.org/talks.htm

You can also search Vimeo for more.