Google for molecules. With a simple interface and super fast search engine, eMolecules augments PubChem with other information sources, including specialty chemical catalogs. Although eMolecules' emphasis seems to be on commercially-available compounds, it's only possible to get a link directly into a supplier's online catalog for a limited number of molecules. Most of the links are to PubChem records. For this reason, I don't find eMolecules very useful in its current form. If you remember something called “Chmoogle”, this is the same service (moral: don't mess with Google).