A site for drawing 2D and 3D structures online. It looks like it will be useful for students, but read the comments under Read More when the warning "The resolved 3D structure can sometimes be inaccurate" appears. It explains when and why the structure might be incorrect. It also explains how to fix potential problems.
This very sophisticated page developed by Otis Rothenberger gives you all the presence of a physical molecular model but with all sorts of additional features. These additional features include the ability to search and load molecules from the protein data bank, PubChem, or the NIH/NCI Chemical Identifier resolver.