PubChem provides information on the biological activities of small molecules.
Developed by NCBI at the National Institutes of Health, the database contains chemical structures, synonyms, descriptions, related urls, database cross-reference links to PubMed, protein 3D structures, and biological screening results.
Here’s an instructional video to help you get started with PubChem.
http://www.youtube.com/watch?v=3pxnq_Q9Tfo
More videos available here.