http://molprobity.biochem.duke.edu/ - Evaluate X-ray structure: Typical steps for a published X-ray crystal structure or one still undergoing refinement.
PDBsum is a pictorial database that provides an at-a-glance overview of the contents of each 3D structure deposited in the Protein Data Bank (PDB). It shows the molecule(s) that make up the structure (ie protein chains, DNA, ligands and metal ions) and schematic diagrams of the interactions between them.