This video is fairly old, from 2008. It was presented by Michael Steil at the 25th Chaos Communication Congress, but it has resurfaced today on Reddit.
It is still the best 1-hour long summary of the Commodore 64 hardware and the perfect introduction for those who want to learn more how the C64 works.
[youtube ZsRRCnque2E nolink]
There is also a companion PDF that can be downloaded following the link below.