With the Next Generation Science Standards inclusion of engineering/design and the Common Core's call for problem-based learning, I think its time to share a website that is a veteran in the STEM open education resource (OER) community.
The website is TeachEngineering. This site hosts standards-based STEM curriculum units that are free to all educators and does not require any membership. Click and download; good to go. The resources were developed by university professors, college students, and classroom teachers through NSF funding. You can search content based on national standards. What's great about this resource is the range of curriculum; there are classic engineering education projects (e.g. bridges, dragsters etc.) as well as many new approaches to carrying out project-based learning through the lens of engineering (e.g. earthquakes, sensors, etc.). Enjoy!