Desirable US Stamp Sets

Two of the most desired commemorative sets in all of United States philatelics are the Columbian Exposition stamps of 1893 and the 1898 Trans-Mississippi Exposition set (the stamp set that includes the famous cattle in the storm stamp). I've read that when the Columbians came out, they were greatly disliked, and that the same was true for the Trans-Mississippi set - because it was supposed to be bi-colored, and when it wasn't, collectors were disappointed. Perhaps part of the reason for the high value of both sets today is that they were not as widely collected as they might have been when issued. Another reason is that even one of the high value stamps of those sets probably represented about what a person in those times made in a day.

The Graf Zeppelin set of airmail stamps is no doubt the most desired - and by far the most expensive - of all the U.S. air post stamps. They are Scott # C13, C14, and C15. Issued in 1930, each features a depiction of the Graf Zeppelin dirigible or airship. If you don't want to spend the bucks for these (a complete set will cost well over a thousand dollars), you can get the "Baby Zep" - Scott # C18 - for far less money.