All lessons relate to aerospace. Most contain free materials that can be requested via snail mail. This site may not be huge, but it's very well-organized. You may have to follow several links before actually getting to the lessons. Science Power 2000 Divided by section and grade.
All lessons relate to earth science.
Columbia Education Center A billion lessons, but it may take some time. Some must be requested through the mail, and some use an on-line form.