A collection of online and offline spectral libraries for the [diy spectrometer](/tool/spectrometer) project:

I believe most of these are either for remote sensing or for astronomy, so sample-based spectral libraries may be different:

* http://vpl.astro.washington.edu/spectra/allmoleculeslist.htm
* HITRAN data for specific molecules: http://archive.publiclaboratory.org/hitran-spectral-library/
* ASTER library for remote sensing/hyperspectral data, mostly land types: http://archive.publiclaboratory.org/aster-spectral-library/