Providers
Modern Interactives
This is for stuff that uses cutting edge web technology in creative and new way.
💯This is a modern platform for interactively showing the results of some research papers
http://distill.pub/
💯Game developer and math nerd, really interactive demos
http://acko.net
A website that hosts a small collection of interactive material
https://academo.org/
A website that claims to show many explorable and interactive projects to illustrate complex concepts
http://explorabl.es/
People!
💯Full length instructional videos covering mathematics, as well as everything else
https://www.khanacademy.org/math
Probably every single piece of math known to man
https://en.wikipedia.org/wiki/Portal:Mathematics
Wikipedia also a lot of great animations from a lot of people
https://commons.wikimedia.org/wiki/Category:Mathematical_animations
https://commons.wikimedia.org/wiki/Category:Mathematics
💯This guy has intuitive explanations of everything ranging from Netflix to calculus and beyond.
http://betterexplained.com
Interactive software based on Wolfram's systems
http://demonstrations.wolfram.com
💯My favorite website, before web 3.0
http://www.falstad.com/mathphysics.html
💯Amazingly aesthetic approach to showcasing mathematics!
http://world.mathigon.org/
Youtubers
WelchLabs
https://www.youtube.com/user/Taylorns34
💯VSauce!
https://www.youtube.com/channel/UC6nSFpj9HTCZ5t-N3Rm3-HA
Numberphile!
https://www.youtube.com/channel/UCoxcjq-8xIDTYp3uz647V5A
💯Minute Physics
https://www.youtube.com/channel/UCUHW94eEFW7hkUMVaZz4eDg
💯Vi is the maker of the famous Doodling in Math Class series, and loves to rant about interesting topics
http://vihart.com/
💯These are very elegant videos walking us through difficult concepts through beautiful animation and classical music accompanying in the background
http://www.3blue1brown.com
Standup Maths
https://www.youtube.com/channel/UCSju5G2aFaWMqn-_0YBtq5A
Singing Banana
https://www.youtube.com/channel/UCMpizQXRt817D0qpBQZ2TlA
Looking Glass Universe is a instructional video series about quantum physics
https://www.youtube.com/channel/UCFk__1iexL3T5gvGcMpeHNA
Mathologer
https://www.youtube.com/channel/UC1_uAIS3r8Vu6JjXWvastJg
Guy has a good intro to tensor
https://www.youtube.com/channel/UCN8wTUlSAroLslWyf87E2pw
This guy helped me out a ton in my stats class
https://www.youtube.com/user/jbstatistics
Libraries
💯This is an encyclopedia dedicated entirely to mathematics, it also has an associated intelligence engine that competes with Watson
http://mathworld.wolfram.com
This is like google, but for it's numbers (integer sequences). Try using it to look up pi (3.14159)
http://oeis.org/
If you ever need to figure out the center of a triangle 12000 different ways
http://www.uff.br/trianglecenters/etcwc.html (Interactive works in IE)
http://faculty.evansville.edu/ck6/encyclopedia/ETC.html
💯this is reddit, no description necessary
https://www.reddit.com/r/mathgifs
https://www.reddit.com/r/mathvideos/
https://www.reddit.com/r/Physicsgifs
💯this is a web form you use if you have a question about math
http://math.stackexchange.com
this is a web forum for people who are really good at math
http://mathoverflow.net
Challenges (problems)
Millennium prize problems, solve one and you will get an AWARD OF ONE MILLION DOLLARS
http://www.claymath.org/millennium-problems
This is like a trivia question website which hosts a sizable range of topics
http://brilliant.org/
Places and organizations
💯Museum of math, located in New York. Has many exhibitions and very kid friendly, they also have a web shop online
http://twitter.com/MoMath1
http://momath.org/
Mathematical Association of America
http://www.maa.org
https://twitter.com/maanow
Books
This is a not so renowned book written by Sanjoy. This book teaches very dirty and quick methods of solving mathematical problems
http://streetfightingmath.com/
This is a very renowned book, written by George Polya in 1945, illustrating the art of teaching how to find a solution to problems, with an emphasis on mathematics
https://en.wikipedia.org/wiki/How_to_Solve_It
http://math.hawaii.edu/home/pdf/putnam/PolyaHowToSolveIt.pdf
The philosophy of this website:
https://www.maa.org/external_archive/devlin/LockhartsLament.pdf
Proofs without words
https://mathoverflow.net/questions/8846/proofs-without-words