PhET Interactive Simulations
Massive collection of excellent (and free!) science and math sims
Bottom Line: Instantly add meaningful lab experiences to math and science classrooms for free? It's tough to beat that.
Learn.Genetics
Dreamland of multimedia resources for budding biologists
Bottom Line: Biology teachers and students will find a lot of useful multimedia here to help them teach and understand complex genetics topics.
NASA Global Climate Change - Vital Signs of the Planet
Tons of climate change info from expert sources in one easy place
Bottom Line: This is a one-stop shop for climate change info, from basic intro content to practical guides and raw data; good for middle schoolers and up.
NOVA Labs
Online science, mastered: exceptional content within meaningful tasks
Bottom Line: Serious, sophisticated science engagement -- but be prepared to take some prep time to connect these labs with your classroom.
Arduino Science Journal
Turn your phone into a lab sensor to collect and analyze data
Bottom Line: Science Journal does a good job recording real-time motion, sound, and light data using phones.
BioDigital
Explore every bit of the human body in this powerful, interactive 3D tour
Bottom Line: This visually stunning, incredibly useful way to virtually explore the human body is a must for the anatomy classroom.
Ptable
Definitive periodic table with all the bells and whistles
Bottom Line: You won't need any other once you have probed the depths of this truly complete reference resource.
OER Project
Expansive world history courses powered by great open-source materials
Bottom Line: A stellar program for exploring foundational concepts in history, humanities, critical thinking, and science with tons of support for teachers.
BioInteractive
High-quality multimedia brings biological research to life
Bottom Line: Superb multimedia tools and lesson plans help kids explore biology through real-world examples.
Kerbal Space Program
Design and launch a rocket into space in realistic astrophysics sim
Bottom Line: This accurate rocket sim encourages trial-and-error learning and makes for great (and often explosive) physics and engineering experiments.