Periodic Table

Tables charting the chemical elements have been around since the 19th century - but this modern version has a short video about each one.

PubChem (NCBI)

PubChem provides information on the biological activities of small molecules. PubChem is organized as three linked databases - PubChem Substance, PubChem Compound, and PubChem BioAssay. PubChem also provides a fast chemical structure similarity search tool.