Desmos offers tons of math resources all in one place! Calculators, lessons and a cool graphing tool that teaches you all about graphing.
Khan Academy is a popular site used for math videos and lessons, bu it has so much more!
PhET is a science and math simulation site that is broken down by content and grade level. It also connects to your Google Classroom.
Plotvar is an easy graph site where you enter calculations and it makes you a graph!
That Quiz is a math quiz site that is great for skills reinforcement.
Virtual Nerd offers tons of math support videos for middle grade through high school students.