This website is the directory of links allowing finding, teaching and learning resources from the federal agencies U.S. This website is the most popular because of the many great resources being offered by contributing federal agencies.
For chemistry it contains 38 links to different types of websites. You can find a lot of information on the links - from interactive description of discoveries in science and technology in 20th century
http://www.pbs.org/wgbh/aso/ to the very nice simulation of chemical processes
http://workbench.concord.org .
It contains interesting videos as well as the interactive periodic table. As the materials range from basic to advanced, some of them require no previous knowledge and have no prerequisites (such as the explanatory video called the chemistry of hamburger), some of them are more advanced and require previous knowledge of certain issues and procedures in order to understand them properly.
The website contains links to different kinds of videos and articles. Many of the videos I find pretty unique as they contain explanation of issues that are quite unusual to be explained in instructive chemistry videos, such as application to foods and other day to day issues. It aims at providing relevant material on different kind of matters. Mostly it aims to create interconnection from different websites on one site, where one can go and find all relevant and necessary information not only in chemistry but also in health, art or science.
It can be used as a material to prepare the lectures or as a study at home guide to turn to when unsure on some subject. The videos can be played during classes as an interesting diversification. Some of the links contain plain text with explanation of the given topic only; these can be used during group exercises as research on the topic or to find answer to some specific question.