Multiple Listing Service online
A comprehensive residential real-estate listing site operated by The Canadian Real Estate Association, albeit not the full MLS database.
Canadian commercial real estate listings
A comprehensive commercial/industrial real-estate listing site operated by The Canadian Real Estate Association.
Urban Land Institute (US)
Nonprofit real-estate forum which aims to facilitate the "open exchange of ideas, information, and experience among local, national and international industry leaders and policy makers dedicated to creating better places."
Official publication of the Urban Land Institute
Official website of the US National Association of Realtors, including listings