Elemental X-ray properties (Materials Sciences Division of LBNL)
Atomic scattering factors (Uppsala University, Sweden)
Compute X-ray absorption (Brian H. Toby, Argonne National Laboratory)
Units conversion (The Ganoksin Project)
X-ray dynamical diffraction data on the web (by Sergey Stepanov, ANL)
X-ray anomalous scattering (Ethan A. Merritt, Biomolecular Structure Center at UW)
Bilbao crystallographic server (tools, space groups, databases; Materials Laboratory at UPV/EHU)
The space group explorer (CALIDRIS)
Crystal LatticeStructures (Center for Computational Materials Science, NRL)