Space Group Tables. Hypertext book of crystallographic space group diagrams and tables.
CCDC Web-Search. Search the Cambridge Crystallographic Database for molecular crystal structures from your browser (advanced search requires login with site license).
Powder Diffraction on the Web. Online course for powder diffraction materials courtesy of Dr. Jeremy Cockcroft and the Department of Chemistry at the University College, London.
Magnetism
PHI. Fitting software for molecular magnetic susceptibility data.