"These pages are full of Snacks...but they're not the kind you eat. They're the kind you can learn from and have fun with. Exploratorium Science Snacks are miniature versions of some of the most popular exhibits at the Exploratorium."
"The Molecular Logic Database is designed to provide teachers and students with easy access to our model-based activities."  Wow - excellent applets for understanding molecules!  Easy to load on your computer.
" is your gateway to experience the excitement of contemporary science and technology through on and offline interactivity with science and technology centers worldwide. Science is exciting, and it's for everyone! That's why TryScience and over 400 science centers worldwide invite you to investigate, discover, and try science yourself."
The Physics Education Technology (PhET) project at the University of Colorado produces fun, interactive simulations of physical phenomena that make bridges to the real world.
Texas Regional Collaboratives for Excellence in Science Teaching
Welcome to the U.S. Geological Survey - federal source for science about the Earth, its natural and living resources, natural hazards, and the environment.
SpaceTEC is a focal point for educators of aerospace technicians.  Aerospace curricula, exams, professional development, & other  resources are provided.
The Space Weather Center explores the solar cycle, solar wind, Earth's magnetic field, the ionosphere, auroras, states of matter, plasma (which makes up 99% of visible matter in the universe), & other sun-earth topics. Online games let students launch solar particles at Earth, bowl with protons, & watch charged particles move in magnetic fields. Information is provided on space weather
research, space weather modeling & forecasting, & the National Space Weather Program.
Julian Rubin provides "a collection of K-12 science jokes and quotes studded with science links, pictures and stamps. The jokes are short, not complicated or abusive and organized by topic."
"The NIH Curriculum Supplement Series are interactive teaching units that combine cutting-edge science research discoveries from the National Institutes of Health, one of the world's foremost medical research centers, with state-of-the-art instructional materials."
Introduction to Watershed Ecology, a training module developed by the EPA.
This collection from the Getty Museum, entitled Devices of Wonder, resides at the Getty Museum website.  Each picture is interactive.

This is the opening text from the website:  "Welcome to the Molecular Expressions Virtual Microscopy Website. We invite you to visit the interactive Java-powered virtual microscopes that we have constructed. These virtual microscopes explore specimen focus, illumination intensity, magnification, and translation---operating essentially in a manner that is identical to real-life microscopes."

How Stuff Works would be an excellent resource for teachers, especially in science.
Powers of 10.  Go from a view of a solar system to a molecule!

The National Space Biomedical Research Institute is just one of the great links out there for science teachers.

Science lesson plans at this site from Teachervision.  Teachers can sign up for a monthly newsletter.
"MicroWorlds" looks at materials sciences research at the Advanced Light Source (ALS), a facility that produces light one billion times brighter than the sun & offers opportunities for studying semiconductors, polymers, malaria, the electronic structure of matter, & other topics.
"Science Education at Jefferson Lab" offers 16 hands-on activities to answer questions such as: How do scientists to measure the size of an atom? What kind of coat will keep you the warmest -- one made from cotton, steel wool, or air? How should you build a boat so that it carries the most cargo?
"Bugscope" offers magnified images of specimens of beetles, spiders, & other insects & anthropods viewed through an electron microscope. (NSF)
"For Kids Only: Earth Science Enterprise" helps students learn about aerosols, ozone, air pressure, tropical rainfall & hurricanes, plate tectonics, earth science careers, & more. (NASA)

Newton " offers an "ask a scientist" service, a question of the week, & resources developed & identified by teachers. (DOE)

"Windows to the Universe" explores the Earth, planets of our solar system, & the universe.  It includes images, animations, & data sets, & information about books, movies, scientists, & myths. (NASA)

"Inquiring Minds" features an introduction to elementary particles & forces in our universe, physics questions answered by Fermilab scientists, an interactive timeline illustrating the history of high-energy physics, links to other high energy physics sites, & more. It is maintained by Fermilab, the high-energy physics lab devoted to studying the universe. (DOE)
"Interactive Plasma Physics Education Experience" offers web modules that help students distinguish atoms, ions, elements, & molecules; understand basic concepts involved with electricity & magnetism; & see how energy flows through different states. (DOE)

"Searching for the Building Blocks of Matter" looks at Fermilab's search for the smallest building blocks of matter. It also describes the accelerator & detectors needed for the discovery of these building blocks (quarks, leptons & bosons), spin-offs along the way, & continuing efforts to reveal the basic particles & forces of nature. (Fermilab is a high-energy physics laboratory that houses the Tevatron, the world's most powerful particle accelerator.)