First of all, The Western Tradition. I remember being enthralled watching the late Professor Eugen Weber explaining the history of Western civilization. Just the good Professor, a podium, and illustrative slides. Not just the dates and important people, but good insight into how people actually lived during that time.
Second, my favorite "how things work" show: The Secret Life of Machines. Simple and fun explanations of how basic and not so basic machines work, with excellent demonstrations.
I highly recommend both of these shows.