Structure Databases:

PDB (Protein Data Bank): http://www.rcsb.org/pdb/

BMRB (Bio Mag Res Bank): http://www.bmrb.wisc.edu/

Structure Visualization:

DeepView site: http://www.expasy.ch/spdbv/

DeepView tutorial: http://www.expasy.ch/spdbv/text/tutorial.htm

Major structural classification websites:

SCOP: http://scop.mrc-lmb.cam.ac.uk/scop

CATH: http://www.biochem.ucl.ac.uk/bsm/cath

DALI/FSSP: http://www2.embl-ebi.ac.uk/dali