Beilstein/Gmelin:

Great databases for chemical and physical properties of all compounds. CRC handbook of Chemistry and Physics is an easier source to use for physical properties of more common compounds.  These databases are best searched by chemical structure.

Beilstein covers organic compounds

Gmelin covers organometallic & inorganic compounds.

Beilstein is useful for chemical and physical properties, synthesis and chemical reactions of over 8 million organic compounds. The Gmelin database covers more than 1.4 million organometallic and inorganic compounds (including coordination compounds, alloys, glasses, ceramics, polymers and minerals), with more than 800 property fields defined.

Available: This database is available on three computers in the Chemistry Library.