Vihart: Though technically an employee of the Khan Academy, Vihart stands alone when it comes to amazing math videos on YouTube. Her hands-on approach to math will be sure to engage even the most reluctant of learners in your classroom.
PatrickJMT: This YouTube EDU guru has been creating straight-to-the-point math videos for over 4 years now. The goldmine of content on his channel is something every math teacher needs in their arsenal of differentiation tools.
Numberphile: Numberphile is just like the a name suggests: a channel where people are obsessed with numbers. They take a look a specific numbers, describe why they are interesting, and how they are come into play in the real world.
Mathalicious: Though this channel is mainly a promotional effort directing viewers to their premium content hosted on their site, the few videos they have are great for getting conversations started in math class.