SpringerMaterials is the successor to the Landolt-Börnstein database, and has additional collections such as the Linus Pauling Files among others. The L-B database alone has over 200,000 entries for crystallographic data. It is recommended to search by formula or structure, and then narrow by the property of interest.
Following a chemical substance search, click on the CAS number to bring up a listing of both calculated and experimental physical and chemical properties. Crystal structure data, if available, is listed under 'Structure-related Properties'. If no specific values are given, references to the literature are usually provided.