IUCR:
www.iucr.org - International Union of Crystallography
it.iucr.org - International Tables
http://www.iucr.org/people/wdc - World Directory of Crystallographers
http://journals.iucr.org/ - Crystallography Journals
http://checkcif.iucr.org/ - CheckCIF
http://www.iucr.org/resources/cif - Everything you ever wanted or needed to know about CIFs.
http://www.iycr2014.org/ - International Year of Crystallography
Associations:
http://www.amercrystalassn.org/ American Crystallographic Association
http://crystallography.org.uk/ British Crystallographic Association
http://www.aps.org/ American Physical Society
http://www.acs.org/ American Chemical Society
Software:
Databases:
Cambridge Crystallographic Data Centre
Inorganic Crystal Structure Database
International Centre for Diffraction Data
Miscellaneous:
X-ray Anomalous Scattering http://skuld.bmsc.washington.edu/scatter/AS_index.html
Space Groups: http://ressources.univ-lemans.fr/AccesLibre/UM/Pedago/physique/02/cristallo/espace.html
Temperature Calibration - http://www2.fkf.mpg.de/xray/html/temperature_calibration.html
ALS X-ray Data Booklet - http://xdb.lbl.gov/
PRODRG2 - http://davapc1.bioch.dundee.ac.uk/cgi-bin/prodrg
Point Group Symmetry Visualizer - http://symmetry.otterbein.edu/gallery/