Aside from our listings of stolen art web-sites  The best source of current information is the mailing list of the Museum Security Network.  (Non-Profit; Netherlands)  It is also a pleasure to assist them as  Contributing US Editor

Archive Museum Security Network
http://te.verweg.com/pipermail/msn-list/

Archive (Old) Cultural Property Protection
http://te.verweg.com/pipermail/cpprot/

Stolen Art & Art Crime:
Files of the LAPD Art Theft Detail
The controversial Michel van Rijn.
Blog Art Stealer
Blog YourBrushWithTheLaw.com
Blog Stolenvermeer.com

Archeological & Cultural Property:
Illicit Antiquities Research Centre
USIA Cultural Property Recent Reports
Archaeology  (a very good Journal)

Art Projects - Conceptual Art:
Body Missing Project (WWII Kunstraub)

Art Crime (the destruction of art)