This interactive Periodic Table of the Elements linked to Wikipedia is done in all XHTML so as to be scalable. Try adjusting your window size to see it adjust accordingly. Here is a non-scalable but equally well executed Table done in Flash and another flashcard type site for testing your memory of where on the table the elements fall. This multimedia table includes videos and demonstrations.
update: Here’s more, ptable, webelements (click symbol for description of elements), ChemReference: Periodic Table and this one from the now infamous britishpetroleum lists products that’s made using each element.