Others have already chimed in here, but I honestly can't remember a CGP Grey video that I wasn't thoroughly entertained by, even when I already knew all of the facts presented.

For amusement's sake, I really enjoy his videos on geography, such as (his first video ever) this one on the UK (which I guess might need updating soon?):

https://youtu.be/rNu8XDBSn10

or this one on Scotland:

https://youtu.be/p3HnMLq8m9U

or my favorite geographical video, on the Vatican:

https://youtu.be/OPHRIjI3hXs

That said, they're all pretty great, so I'd just start with this list of all his videos in ascending order:

https://www.youtube.com/watch?v=rNu8XDBSn10&index=1&list=PLq...