Are there any free phosphorus-31 NMR spectral libraries? I know that there are some sites like Sigma Aldrich and AIST for $\ce{^1H}$ NMR and $\ce{^13C}$ NMR, but was wondering if there were any free sites to compare $\ce{^31P}$ NMR spectra?
There are quite a few it seems, a couple of examples are below:

University of Wisconsin Phosphorus NMR data, starts with a shifts overview.

Stanford's Magnetic Resonance Laboratory site P NMR at the SMRL, provides comparisons and a protocol for testing.

A general NMR site is NMR Wiki - has many links to many sources.