All links are to videos tab on YouTube page, rather than home page. This is just due to my preferred habits when YouTube browsing.

CGP Grey covers loads of topics, only releases videos rarely, and every one of them is amazing.

Cody'sLab is a backyard chemist / scientist / miner / metallurgist / apiarist. If you're a fan of scientific methods and process, this guy shows that a bit of sense and a DIY attitude can get you everywhere.

CrashCourse covers a bunch of topics to moderate depth. Prob check the Playlists tab on a completed series for a first look.

DeepSkyVideos if you space.

Kurzgezagt - In a Nutshell is another page that doesn't post videos very often, but when it does, it's amazing.

Mark Rober is an ex-NASA engineer who does fun stuff like show you a DIY video on how to turn a leaf blower into a snowball machine gun.

Numberphile for math nerds. You nerds.

Objectivity 'cause Keith is a dapper gentleman and old stuff is interesting.

Periodic Videos for chemistry nerds. You nerds.

Physics Girl is hit or miss, to be fair, but some really good stuff in there. Plus, cute hawai'ian women are rockin'.

SciShow for daily shorts with science news content.

SciShow Space is same, but more space themed, so not daily.

Sixty Symbols used to be great. The deep catalog is really good, but they've lost their direction.

SmarterEveryDay for that southern gentleman scientist dad guy fix.

TheBackyardScientist is a guy who throws bullets into molten aluminum in his backyard in a Florida suburb among other things.

The Slow Mo Guys do slow motion videos.

Veritasium is another kind of random science dig channel.

Vsauce is similar, but more broad and unpredictable in topic - bit like Kurzgezagt.