The PhET website (Physics Education Technology), is a source of great Interactive Simulations for Math and Science. Many of the simulations can be easily EMBEDDED into your class site. Unfortunately not all of the simulations are able to be embedded directly, as they are .jnlp files, which run on java script (such as the Acid / Base Simulation), but you can link to them from your page with an easy picture link that they provide.
To EMBED one of the simulations into your own page, you will need to find a simulation on the PhET page that you would like to embed, and then click the EMBED option. This will bring up the code, and you can either grab the IFRAME code if your site supports it, or if you use WordPress which does not support IFRAMES, then you can grab the second code which will allow you to put a direct link in your page.
These simulations are great for Math or Science, and could be used as a quick way for students to grab data sets for manipulation that they might not be able to generate in your own lab.
Here are a few example simulations that are embeddable in your page!