NIST Webbook -- IR, Mass Spec, NMR, UV/Visble & Vibrational spectra. Searchable by formula, name, CAS registry number, molecular weight, ionization energy or proton affinity. Contains a full array of data compiled and distributed by NIST.
SDBS--IR spectra -- Integrated Spectral Data Base System for Organic Compounds from National Institute of Materials and Chemical Research, Japan. More than 47,000 IR spectra are available, as well as thousands of 1H and 13C NMR, MS and ESR spectra.
spectrometryNOW --The web's leading mass spectrometry resource (registration (free) required for access to some links)
PROWL -- a resource for protein chemistry and mass spectrometry
Last updated: January 16, 2008