8th Annual Report to Congress on Carcinogenic Compounds Database covers all known and suspect carcinogenic compounds with including listing by CAS number
Chemical Information by name, CAS etc. Search page for information about a wide range of chemicals includes molecular information, molecular model, sources, MSDS, and vast amounts of related information through links.
OSHA Ventilation Page covers wide range of ventilation related topics in areas such as recognition, trouble shooting, etc.
Agency for Toxic Substances and diseases Registry (ATSDR) Chemical ToxFAQs sheets Gives descriptor for a wide range of chemicals including: what they are, their effects on humans, what happens when they enter the environment, degradation by products, etc. Helpful page for monitoring a cleanup activity.