50 Really Cool Online Tools for Science Teachers: Self-explanatory. : )
100 Best Websites for Science Teachers: 'Nuf said.
Middle School Science: Scads of links from Jefferson County Schools, TN, to general, physical, earth, and life science sites. Many seem adaptable to other ages.
PBS STEM Resources for Kids: Links to PBS sites related to STEM.
STEM Resources: Several pages of an Edutopia.org discussion of science teachers posting their favorite STEM online resources.
USGS Education: Site built by the USGS with some super resources!
Kids Online Resources, Science: 4 pages of more science sites than you can shake a stick at! Ideas for science fair projects, too.
Kathy Schrock's Guide for Educators: Links to every field of science. Enough to melt your brain!