www.webelements.com ... an online Periodic Table, with lots of useful information about the elements!

NIST Chemistry Webbook (good source of thermodynamic, spectroscopic data)

Fundamental Constants (NIST)

Nomenclature (IUPAC)

Miscellaneous chemistry links (Liverpool)

NIH Molecules to Go (database of biological molecules)

NIOSH Pocket Guide to Chemical Hazards (safety info)

Crystal Lattice Structures (Naval Research Laboratory)

Orbital Viewer (for download)

American Chemical Society

Periodic Table of Comic Books (just for fun!)

Columbia Chemistry Library

Barnard Chemistry Department

Columbia Chemistry Department

Barnard Chemical Society

3D MolSym (for visualizing symmetry elements)

Periodic Table Quiz

Molecular Vibrations (UCLA)

The Inorganic Web (Minnesota-Duluth...visualizing orbitals, VSEPR, packing...)

Rotatable Images of Atomic Orbitals (Minnesota-Duluth)

Chemical Waste Disposal (Princeton)

Symmetry (Otterbein College)

If you come across other links you find useful, and you would like me to post them here, send me the URL!