PhET Science Simulations

If you haven't used the PhET simulations with your class, you are missing out!  These are great simulations for all areas of science.  I love them because there are some times when setting up an actual lab is not possible and these simulations provide students with the experiences to understand the concept.
PhET was Java based, but are not moving into creating simulations that run on HTML.  What does that mean?  They will not run on machines that don't have Java such as iPads and Chromebooks.  Even better, there is a page where other teachers have submitted their lesson plans and worksheets that go along with these sims; so everything is practically done for you!
They are even in the process of developing a Teach with Sims page to help you out more.  You can check out the prototype that they have already developed.

What other computer sites do you use in your classroom?