Websites on Undeveloped or Vacant:
Land Watch
Site listing rural land in North and South America.
LandFlip
Listings of lots and acreage for sale, land auctions and rural retreats.
Land.net
Directory of residential and commercial land for sale or lease.
Private Islands Online
Offers listings of islands for sale or rent in the US, Caribbean, Canada, Oceania, and Europe.
Realtors Land Institute (RLI)
Organization of professionals specializing in land brokerage. Includes details on membership, property search, and an auction calendar.
UK Land Investments Group
Develops parcels of undeveloped land from offices around the globe; includes investment opportunities, market statistics, and news.