Alan Kay has got to be one of the smartest people alive. I wish he wrote more. My favorites are his answer to the question "What do you believe is true, even though you cannot prove it?":

http://www.edge.org/q2005/q05_8.html#kay

and his essay "Predicting the Future":

http://www.ecotopia.com/webpress/futures.htm

His other work is quite impressive, also, but these two are by far my favorites.