Enter a chemical name, draw a chemical structure (substructure, similar, or exact match), or upload a structure, and Chemicalize.org will search the Web for pages that have been chemicalized. The result contains structures and the Web pages that include the target structure. It is also possible to find properties. Check out this video for a quick demo.
ChemSpider can be used to search, aggregate, and data mine publicly available chemical information, including data from PubChem. It can be searched by exact structure, substructure, and similarity structure as well as by chemical names and molecular formula, and limited by properties. ChemSpider has been enhanced with calculated properties from ACD Labs. ChemSpider provides access to over 32 million structures along with properties and associated information.
Formerly Chmoogle, eMolecules is a chemistry search engine. Draw and enter a structure or substructure; or enter a systematic, standard, common, brand, or chemical name, and eMolecules quickly searches over 6,000,000 substance records from sources like PubChem and vendors catalogs.
Wolfram|Alpha is an excellent resource for finding chemical information such as unit conversions, flash points, thermodynamic properties, reactivity, and boiling points. It also provides rapid and accurate computations. Examples of chemical information found in Wolfram|Alpha are available here.