Building Big is a great site from PBS that has lesson plans, projects, labs, and activities for teachers to use in their classrooms. The topics are on buildings and structures, including Bridges, Domes, Skyscrapers, Dams and Tunnels. It's based on the PBS television series Building Big.
There are interactive labs, educator's guides, challenges, data on the world's structures, and information about engineering and engineers.
The labs are flash-based interactive activities that let students explore forces, materials, loads, and shapes and get information about each topic.
The activities are fun and educational and the resources can be scaffolded for any level.
STEM Resources for Educators
Project Based Learning resources for Educators