The NIST (National Institute of Standards and Technology) Standard Reference Databases provides valuable resources. Two resources were specifically mentioned by respondents to the 2013 Inorganic Curriculum Survey: the webbook and the stability constants of metal complexes. Some of the data in the Chemistry WebBook include
- gas-phase ion thermochemistry
- organometallic thermochemistry database
- vibrational and electronic energy levels of polyatomic transient molecules
- evaluated IR spectra & quantitative IR database (limited)
- UV/VIS database
This is a nice resource if you need to look up physical data. The Stability Constant Database is no longer supported.
Other NIST resources that may be of interest to users include the Thermochemical Tables, Physical Reference Data and more! The NIST resources are definitely worth browsing through.