IUPAC Compendium of Chemical Terminology: The online version of the "Gold Book" which collects together terminology definitions from IUPAC recommendations published in the journal Pure and Applied Chemistry and in the other Colour Books.
IUPAC Nomenclature: This site, based at Queen Mary, provides information on IUPAC recommendations. The full-text of many of the recommendations is also available here.
Interactive Periodic table: “The Royal Society of Chemistry's interactive periodic table features history, alchemy, podcasts, videos, and data trends across the periodic table.”
WebElements: The periodic table of the chemical elements on the web.
Organic chemistry/Inorganic chemistry
Macrogalleria: Provides a wealth of information around polymers, created by the University of Southern Mississippi.
Molecule of the Month: As the name suggests, every month a link to information about a new molecule is added to this site. An alternative collection is available at com.
Organic Chemistry Portal: Offers an overview of recent topics, interesting reactions, and information on important chemicals for organic chemists.
Organic Synthesis:Provides detailed, reliable, and carefully checked procedures for the synthesis of organic compounds.
Organometallic HyperTextBook: This site, created by Rob Toreki, is designed as a reference tool for students that are starting out in the area of organometallic chemistry. It includes information on a wide range of topics as well as links to other useful Internet resources.
Analytical Sciences Digital Library:This site, funded by the US National Science Foundation (NSF), provides a collection of peer-reviewed analytical science resources for researchers, teachers, students, and interested amateurs.
Crystallography 101: Interactive learning resource around protein crystallography created by Bernhard Rupp.