In this blog series (Part 1, Part 2, Part 3) James Hague takes something that would be hopelessly theoretical for most--writing a video game in a purely functional style--and makes it concrete and accessible.
He's actually done the legwork (brainwork?) and thought through the many thorny issues that would hopelessly ensnare programmers that are just getting started with functional languages and the "functional mind-set".
Very, very interesting. A great series, with hopefully many more installments to come.