"Symmetry and space group tutorial" Jerry P. Jasinski and Bruce M. Foxman.
JAVA applet on Bragg's law and diffraction by Konstantin Lukin.
Crystalline Insights: X-ray diffraction and crystal structure determination. Michael J. Vela, Tae H. Cho and Bruce M. Foxman.
Disordered structure refinement with SHELXL by Peter Müller and twinning tutorial by Regine Herbst-Irmer.
A list of Nobel prices associated with cristallography.