Chemical Abstracts (General Chemistry)
SciFinder Scholar

Science Citation Index (General Science)
Based on citations.

Beilstein (Organic)
Needs special software. Searchable from Chemistry, Biology & Engineering Libraries.

Gmelin (Inorganic)
Needs special software. Searchable from Chemistry, Biology & Engineering Libraries.

Inspec (Physical)

Medline (Medical, Biomedical, Biochemistry)
NLM, Medline [Ovid], Enzyme Database (NEW)

Misc: Books in Print, Dir. Grad. Research, Ingenta, Dissertations, More

Undergraduate: General Science Abstracts ~ Applied Science & Technology ~ Proquest Direct ~  McGraw Hill ~ Britannica ~ Kirk Othmer Encyclopedia of Chemical Technology ~ Ullmans Encyclopedia of Industrial Chemistry