Virtual textbook by Stephen Lower.

by David Hsu.
This site also has extensive information on the discovery and uses of each element.

From WebElements.

The history of the development of the Periodic Table.

Annenberg Learner

This site includes posters for purchase like the one above.

From Royal Society of Chemistry.
This site also has information on the history of the Periodic Table and an interesting section on Alchemy.

Great resource! From The University of Sheffield.
The WebElements scholar edition aims to be a high quality source of information on the WWW about the periodic table for students. You will find many pictures showing element structures and periodic properties.

Even with new elements in hand, scientists are struggling to predict the future of the iconic chemical roadmap. By Devin Powell, Smithsonian, January 2016.

"In our daily lives, we rely on many metals that are either uncommon, environmentally damaging, or located almost solely in places like China, Bolivia, or the war-torn Democratic Republic of Congo (i.e., not nations the U.S. is always on good terms with). What's the risk that one day we won't be able to depend on any of these elements?
That's the question asked by researchers from Yale University, who have now catalogued how much we’re in danger of putting all our eggs in one basket. By Jessica Leber, April, 2015