Illuminations has lesson plans and interactives for the Pre-K – 12th grade math teacher, all free!
Sponsored by the National Council of Teachers of Mathematics, Illuminations has over 700 lesson plans and over 100 interactives available. There are also 13 Calculation Nation® games, which are games where the student can compete against other students. If you are an iPad or Android school, they also have 7 mobile apps available. To help you select the content you need, there is a search engine that lets you narrow down the type of content.
Illuminations looks like a great resource for math teachers!