The TV show said to be the most commonly recorded on a TiVo is the hackers' special, Junkyard Wars. Two teams of tinkerers race against each other to construct a working submarine, or an airplane, or a cannon, or deep-sea diving gear, all assembled from scrap found in a junkyard, and all built within a day and a half. That both sides usually succeed at some level (although only one side wins) is the first surprise of this TV series. More amazing is the easy lesson in physics and engineering each episode brings. By watching how a pump is cobbled together from motorscooter tires, one gets a visceral sense of how a pump works. By watching how geeks think around impossible obstacles, one catches the confidence to tackle an impossible project. They are educational enough that some science classes show them.
Episodes available, for example:
Junkyard Wars: Cannons Video #187435
Junkyard Wars: Flying Machines Video #187450
The Discovery Store