What resources are available for any grade level K- 12 that are aligned with the Common Core Mathematics Standards and Mathematical Practices that have sets of problems or problem banks that can be used by teachers for instruction or homework?
Can we include rich math tasks in our answers? If so, look at:
The CME Project! It's a full four-year high school curriculum.
David Wees already mentioned in but I'd like to highlight Illustrative Mathematics - it's designed precisely for this purpose. (It's the brainchild of Bill McCallum, one of the lead authors of the Common Core math standards.)
The Khan Academy has been developing a common core map. They have been working with Smarter Balanced and Illustrative Mathematics on the project.