PhET provides fun, free, interactive, research-based science and mathematics simulations.
CK-12 has many Physics and Chemistry Simulations and PLIX (Play, Learn, Interact, Xplore) activities as well as FlexBooks and adaptive practice modules
NetLogo, a programming language designed to model massively parallel systems (falling leaves, flocking birds, ants foraging for food). Use simulations already created or program your own. Example Autumn
Celestia – Space simulation that allows you to explore the universe in 3D.
Edheads.org is great virtual surgery/engineering site – many of the activities are 6-12
Biodigital Human – virtually manipulate body systems – log in with Google
Virtual and Augmented Reality
Google Expeditions – Check out the kit from Julia Hood
Anatomy 4D by Daqri (the Body, the Heart)
Elements 4D by Daqri
Aurasma – create your own Augmented Reality experience