pElement is an awesome periodic table app for Windows
Even better is pElement, a free application for Windows that packs loads of information into an easy-to-use interface. Click an element and the info window appears, displaying its abbreviation, full name, periodic number, and atomic weight. Need more info? Click an icon to display its physical properties, crystal structure, electron information, and more. Everything from half life to boiling point is within easy reach.
Back to the main window -- pElement also allows you to view elements by their class and form and includes a search function. The extras window includes a handful of useful info like a list of universal constants and superconductors, metric prefixes -- even a unit conversion tool!
pElement is a free download from Crystal Mountain Software.