Some online resources I found useful:
The Basics of NMR by Joseph P. Hornak, Ph.D. at the Rochester Institute of Technology.
Advanced Spectroscopy Lecture Notes by Prof. Dr. Oliver Zerbe at the University of Zurich.
NMR Lectures by Prof. G. Moyna at the University of the Sciences in Philadelphia.
NMR Lectures by Dr. Nagarajan Murali at Rutgers.
Great NMR Blog by Glenn Facey, the NMR Facility Director at the University of Ottawa.
Stan's NMR,MRI,NQR and ESR links
NMR Lab in the Hebrew University of Jerusalem
NMR Artifacts from Michigan State University.
EasySpin: a Matlab toolbox for simulating and fitting EPR spectra.
Links to some NMR groups I like to follow:
Prof. Tim Claridge's Lab at the University of Oxford.
Manchester NMR Methodology Group. They developed many pulse sequences for small organic molecules.