Mathematical Association of America
The MAA has a lot of information and allows those with mathematical background to reach out and share ideas with one another and becoming a member opens up a lot of opportunities to become involved in this association.
Desmos
Desmos is the perfect tool to use in the classroom. Once students become familiar with this app, they will realize it is more than just a graph to plot points. Not only is it a website, but they also have a smartphone application version available as well, which is helpful for students that may not have their graphing calculator.
National Council of Teachers of Mathematics
NCTM is a great resource for teachers who have a background degree in mathematics to become a member of. This is where teachers can share their mathematical ideas and share resources with each other to be utilized in the classroom.
Cool Math 4 Kids
Cool Math 4 Kids is a great online tool for younger students to get interested in math and even offers games for them to play based on math topics.
Math is Fun
I personally have used Math is Fun quite often as it has a ton of information that is beneficial to break down certain topics and gives examples to explain in the classroom. This is also a great resource for students to have as well.
NYS Common Core Math Standards
The basis of lesson plans today are focused around NYS common core curriculum. Therefore, teachers can look online and have access to various types of lessons based on the specified grade.
Kids Math Games
Another website for students to be able to play while also learning math. I would like to use games as much as possible with my students since most students have difficulty with math. I want them to see it can also be a fun thing to do rather than just filling out worksheets.
Purple Math
Purple math is another good reference site that can be used. It is full of mathematical information and will break down a topic in order to get a better understanding.