Sites listed here are recommendations from other teachers –
Just wanted to share that if you haven’t checked out Desmos.com you definitely should. It is a graphing tool that allows you to type in a function and it will instantly graph it for you. You can also type in coordinate points and they will be graphed as well. If you have access to computers, you can have students explore different functions and see what effect it has on the line. As an example: what effect does changing a function from y=3x + 2 to y=3x + 10 have on the appearance of the graph.