Useful links

Periodic tables of elements
Les éléments chimiques (Stéphane Pereck)
Periodic Table (Royal Society of Chemistry)
Element scarcity (EuChemS periodic table)
NMR spectroscopy, analytical chemistry
Spectral database for organic compounds (AIST, Japan)
nmrshiftdb2 (Uni Köln)
NMR spectroscopy (Hans J. Reich, University of Wisconsin)
NMR analysis (Carlos Cobas)
University of Ottawa NMR blog (Glenn Facey)
Mass spectroscopy - fragmentation patterns
Online calculations and simulations