This is Stephen Lower's General Chemistry sources. There are many up-to-date links to general chemistry tutorials, problems, answers, and disquisitions designed for first-year chemistry students.
The Chemistry Hypermedia Project has many web resources for chemistry education professionals.
This is the Computational Chemistry List. It started in 1991 as an FTP list, then went to gopher, and later supported by the Ohio SuperComputer Center and NSF. Plenty of computational aids from several sources are here. Look in the software archive. There are also applications for Macs.
Welcome to the ACSWeb from the American Chemical Society. This is the official home page of the American Chemical Society. Registration is requested not not required. Most ACS links will be active without registration.
The CORRECT (!!) version of the modern Periodic Table: WebElements. Elements through 118 have now been discovered, including #117 just synthesized in 2011
How to tell if your periodic table is the "correct" one Look just below element 39 - yttrium. If 71Lu is there - first element in the d-block - then your table is correct. If 57La is there, or something else, then get a different table: lutetium is a d-block element and lanthanum belongs in the f-block.
The Duke University site also has many WWW chemistry resources.
Diagonalize a matrix! Note: Because of the way the matrix equations are solved, you have to set x = -(eigenvalue). So just change the signs of the eigenvalues and you'll get the correct x values for the Huckel energies.
Finally, NIST, the National Institute of Standards and Technology has, among other things, an atomic clock down-link that will allow you to keep your computer's clock exact.
ChemWeb: jobs, Beilstein Abstracts, much more.
ISIS/Draw: free for academia. Chime is also available.
National Library of Medicine: (PubMed, Medline, Cancerlit)
MSDS: Material Safety Data Sheets - from Sigma-Aldrich
MSDS: more MSDS - from Fisher
MSDS: from the University of Vermont (SIRI)
FDA, U. S. Patent & Trademark Office, Environmental Protection Agency