Here's a list of the YouTube channels I'm subscribed to. It spans a broad range of interests; hopefully you'll find at least some of them interesting.
* Julian Illet - Low-voltage electronics
* Big Clive - High-voltage electronics (plus completely random stuff)
* Cody's Lab - Science of various sorts
* Nile Red - Home chemistry
* Periodic Videos - Professional chemistry
* Tom Scott - Things You Might Not Know
* Objectivity - Brief looks into the archives of the Royal Society
* Numberphile - Mathematics
* Matthias Wandel - Woodworking
* Matt Parker / StandupMaths - Mathematics
* Every Frame a Painting
* James May the Reassembler - BBC show (not a channel, but people have posted episodes) where James May reassembles things that have been disassembled.