Longtime member of the open education community Saylor.org is announcing the release of K12 open courses.  From an e-mail announcement:

K12. Is. Here.
It’s true! Last week, we announced the launch of our new K-12 program of open online courses. The academic courses are aligned to the Common Core State Standards and use open educational resources (OER) extensively, making the courses, as well as their contents, widely reusable by students, teachers, and parents nationwide. Learn More
The K12 Courses can be found here and below are just a few ways to use and reuse our courses. Please feel free to share widely and let us know if you have more creative ideas to add to our list via tweet, facebook or email.
Teachers:

  • Flip your classroom without shooting your own videos.  We already went through and chose our favorites!
  • Incorporate more engaging digital content in your class.

Schools:

  • Get current, Common Core-aligned materials for free. (Almost better than free lunch)

Parents:

  • Provide extra resources to supplement what your kids learn in school.
  • Self-contained curriculum for home school families.
  • Accelerate or review subjects with your kids

Students:

  • Do more challenging work. Your school might not offer Calculus, but Saylor.org does!
  • Learn subjects in a different way and acclimate to an online learning environment.
  • Review material you learned in school.
  • Go further and prepare for your SATs/college (more on that on the site)

Saylor.org also has a wide range of university-level open courses, many built using MIT OpenCourseWare materials.