Marilyn Burns' Site-informative blog, videos, assessment tools, etc.
Engage NY Math curriculum
There is a lot of information linked below on the structure, mathematical practices that are embedded into the lessons, how to support struggling learners, tools used, etc.
Math Professional Development
Math Coach's Corner–This is my favorite math blog; lots of great activities for the classroom and the theory behind best practices!
Achieve The Core-professional development to accompany Common Core State Standards