Numberphile - link
Videos about numbers - it's that simple. Videos by Brady Haran
3Blue1Brown - link
3blue1brown, by Grant Sanderson, is some combination of math and entertainment, depending on your disposition. The goal is for explanations to be driven by animations and for difficult problems to be made simple with changes in perspective.
standupmaths - link
I do mathematics and stand-up. Sometimes simultaneously. Occasionally while being filmed. (It's quite the Venn diagram.)
Derivando - link
Aprende matemáticas de forma divertida. Descubre todas las curiosidades que rodean las mates con Eduardo Sáenz de Cabezón. Cada lunes y miércoles en Derivando.
singingbanana - link
Mathematician, juggler and comedy nerd - but not necessarily in that order.
PBS Infinite Series - link
Mathematician Tai-Danae Bradley and physicist Gabe Perez-Giz offer ambitious content for viewers that are eager to attain a greater understanding of the world around them. Math is pervasive - a robust yet precise language - and with each episode you’ll begin to see the math that underpins everything in this puzzling, yet fascinating, universe
Vihart - link
Vi Hart likes triangles! AND APPLES!