SDBS, spectral database of Japan's National Institute of Advanced Industrial Science and Technology (AIST)

An overview over references for Raman spectra and mineral-related databases

The RRUFF database of Raman spectra, X-ray diffraction and chemistry of minerals

Programs and spectra from John Bertie (quantitative IR spectra of liquids, incl. water)

Database of UV/VIS optical constants of solid materials at Ioffe institute, another website with optical constants - Reference data for XP and Auger spectra

XPSsimplified, a starting point for XPS data interpretation

The NIST XPS database

Search for IR, NMR and mass spectral signals

Calculates isotope distribution in mass spectra

ChemoSpec, an R package for exploratory chemometrics in spectroscopy