The Robert A. Siegel auction firm has been a world leader in the sale of major stamp and cover rarities since the 1950s. Since 1964, they have held their annual Rarities of the World Auctions which have featured practically every important rare stamp in the world over the past four decades.
In April, the Siegel firm uploaded the auction listings and high quality full color images of every auction lot ever offered in their Rarities sales dating all the way back to that first Rarities auction in 1964. It even includes the Rarest Stamp in the World that was auctioned by Siegel in 1970.
This is a tremendous undertaking and is one of the finest free informational projects ever offered to the stamp collecting public. If one is looking for both information and color images of nearly every key rarity under the sun, it may be found at the Siegel website: http://www.siegelauctions.com/rarities.htm