ChemSpider versus SciFinder for finding chemicals without CAS number
SciFinder is a product of Chemical Abstracts Service (CAS), which is a division of the American Chemical Society. Its registry contains information on more than 111 million organic and inorganic chemical substances, and is updated with 15,000 new substances daily. Additionally, it has more than 66 million protein and nucleic acid sequences.[1] The chemical information is produced by CAS, and is prepared by the CAS Registry System, which identifies each compound with a specific CAS registry number, index name, and graphic representation of its chemical structure.[2]

ChemSpider is a free chemical database from the Royal Society of Chemistry. Its registry contains information on 49 million chemical structures, coming from 513 sources. You can search the database by systematic names, synonyms, trade names, database identifiers, and also using structure-based queries, with the option to draw structures in the web page or use structure files from your computer.[3]

Both registries allow you to find literature references, experimental and predicted property data (boiling and melting points, etc.), commercial availability, and spectra,[3] but the CAS registry also offers preparative methods and regulatory information from international sources.[1]

SciFinder may offer more, but it's extremely expensive. In fact, I'm not even sure if CAS offers SciFinder to individuals. You can see their pricing options here. Taking into consideration everything ChemSpider can do and the fact that it's free, it's an excellent resource, and I definitely recommend it.



References


CAS, Chemical Substances   
Wikipedia, CAS Registry  
ChemSpider