Collaborative Teacher sites:

Save time and sign up because you get emails to let you know about recommended resources or free downloads.

TES  (from UK)

Share My Lesson (also from TES but US based)

http://learnzillion.com/

Teachers Pay Teachers - 10 free downloads every week!

CK-12 Foundation

Individual Teacher created sites and activities:

• Activeprompt (Riley Lark)
• Estimation 180 (Andrew Stadel)
• Graphing Stories (Dan Meyer and BuzzMath)
• Math Mistakes (Michael Pershan)
• Math Recap (Dan Meyer)
• Welcome to the Mathtwitterblogosphere (Sam Shah)
• http://pinterest.com/robertkaplinsky/    http://robertkaplinsky.com/lessons/ 
• Visual Patterns (Fawn Nguyen)
• foldables for 6-8 grades (Mrs. Stoltz)
• Collective Memory Activities (Mr. Barton)
• Dan Meyer's Three Act Tasks (Dan Meyer) http://blog.mrmeyer.com/  http://www.101qs.com/ 
• http://mathandmultimedia.com/geogebra/ (by Guillermo Bautista) tutorials on how to use Geogebra
• http://mathandmultimedia.com (by Guillermo Bautista)
• http://harveyshomepage.com (smartboard lessons)
• http://emergentmath.com/my-problem-based-curriculum-maps/  (by Geoff Krall) tons of lessons already aligned to Common Core!  3rd - high school
• http://www.dailydesmos.com/ (Michael Fenton) High School - graphing
• http://msmathwiki.pbworks.com ; http://cheesemonkeysf.blogspot.com 
• http://www.smartboardgoodies.com/  by Amber Coggin  - look under the Math tab for tons of Smart Board tools, activities, and more!
• https://www.facebook.com/BrainyMiscellany  - lots of problems to use in your classroom - some for warmups and many for a class period
• Eric Milou K-12 Mathematics Links

Facebook pages:

https://www.facebook.com/CommonCoreMathResources?ref=stream

https://www.facebook.com/BrainyMiscellany?ref=stream