Periodic Table (freshney.org) is much more than just a periodic table. This program is absolutely jam-packed with features and would be a tremendous resource to any chemistry student.
The program's interface is not the most beautiful we've ever seen, and the program's creator admits on the Help page that it's gotten a little unwieldy as he's added more features. Still, it's worth it to take some time getting acquainted with everything this program has to offer. Although the online Help file is well-written and thorough, it's easy enough to get comfortable with the program just by exploring its many features. And oh, what features there are. Yes, there is the basic periodic table, but this program is a lot more than just a periodic table. Where do we even begin? You can view photos of each element, look at atomic structure diagrams, and check out a world map that shows which elements are found in each country; read biographies of a large number of historic chemists and look at electron configuration tables; and view element tables sorted by electrical properties, thermal properties, hardness, and more. You can also check out a glossary and plenty of other resources to help with chemistry-related problems. And really, we've barely scratched the surface. All of the program's features are easy to access and, despite the sheer number of them, are fairly well organized.
Periodic Table is free. It installs desktop icons without asking but uninstalls cleanly. We highly recommend this program to all users.