The British Guiana 1c magenta is regarded by many philatelists as the world's most famous rare stamp. It was issued in limited numbers in British Guiana (now Guyana) in 1856, and only one specimen is now known to exist. It is the only major postage stamp ever issued that is not represented in Britain's Royal Philatelic Collection.
The Bull's Eye (Portuguese Olho-de-boi) postage stamps were the first stamps issued by Brazil, on 1 August 1843, having face values of 30, 60, and 90 réis. Brazil was the second country in the world, after the United Kingdom, to issue postage stamps valid within the entire country (as opposed to a local issue).
The Inverted Jenny (also known as an Upside Down Jenny, Jenny Invert) is a United States postage stamp first issued on May 10, 1918 in which the image of the Curtiss JN-4 airplane in the center of the design is printed upside-down; it is probably the most famous error in American philately.
The Mauritius "Post Office" stamps were unknown to the philatelic world until 1864 when Mme. Borchard, the wife of a Bordeaux merchant, found copies of the one and two pence stamps in her husband's correspondence. She traded them to another collector.
While they aren’t the rarest or most expensive collector’s item, Penny Blacks hold the distinction of being the first adhesive stamp used by a public mail system. First issued in Britain on May 1, 1840, Penny Blacks feature a distinctive black face and a profile of Queen Victoria.
In 1855, Sweden issued its first postage stamps, in a set of five values depicting the Swedish coat of arms, with denominations ranging from three to 24 Swedish skillings. The three-skilling stamp was normally printed in a blue-green color, with the eight-skilling stamp being printed in yellowish orange.