Another in my loose series of great science-imagery websites: visit http://periodictable.com/ for an illustrated, interactive Periodic Table of the Elements. Hover your mouse over any element for a picture and basic facts or click for more information and pictures. It’s more fun than it sounds, since the graphics are great and all of the information is solid but some of it is quirky. Ages: 9 – 90.
Geeks will appreciate the fact that the website’s author, Theodore Gray, is responsible for the user interface of Mathematica. He has an interesting background essay to the Periodic Table site here; as someone said, it is inspirational in a sobering kind of way.