All IRB Laws of the Game can be found here.
From time to time, National Unions request clarification of laws from the IRB. When the IRB completes the clarification, they distribute the document, and send back to all nations. These can be very important, as they clear up issues with laws and interpreation of laws. They must be read and understood, similar to actual laws, by coaches, players, referees, and spectators. You can find a listing of all law clarifications here.
Often the IRB release memo's on key areas of the game that require attention. The most recent Memo's from the IRB are listed here. 101129 DC COU SM IM10 Council Decisions.pdf 110601 PO Key Areas Memo.pdf 110804 Memo Dangerous Tackles - August 2011.pdf 110121 IRB Memorandum re Dangerous Tackles (High Tackles).pdf 110121 IRB Mémorandum relatif aux Plaquages Dangereux (Plaquages Hauts).pdf 130103 SG IRB Note to Unions on Scrum Engagement