I found a great source for science information I mention it here and on my blog.
Most of the content is free. Some has a small fee. I was able to get some great information about the Apollo Space Program.
From their website:
"Educators need efficient and reliable methods to discover and use science and math materials that will help them meet the demands of instruction, assessment, and professional development in an increasingly complex technology-based world.
NSDL was established by the National Science Foundation (NSF) in 2000 as an online library providing access for users to exemplary resources for science, technology, engineering, and mathematics (STEM) education and research.
NSDL provides an organized point of access to high-quality STEM content that is aggregated from a variety of other digital libraries, NSF-funded projects, and NSDL-reviewed web sites. NSDL also provides access to services and tools that enhance the use of this content in a variety of contexts. NSDL is designed primarily for K-16 educators, but anyone can access NSDL.org and search the library at no cost. Access to most of the resources discovered through NSDL is free; however, some content providers may require a login, or a nominal fee or subscription to retrieve their specific resources."