The revenue stamps of the United States offer numerous sub-specialties for collectors: There are the stock and document transfer tax stamps, the vice tax stamps, and the special services tax stamps. Among the most interesting of this last group are the Consular tax stamps. Scott lists 40 main varieties that were issued from 1906-1952. These stamps were issued to various US consular offices abroad and paid for such things as visas. They often have cancellations from the foreign offices from which they were used. The stamps are all quite scarce, and a collection by cancellation type would offer tremendous philatelic interest for not much money (the reason the cost would be low is that the stamps are so scarce that, after acquiring the basic stamps, it would be unusual to find something that you needed). As luck would have it, we are offering a complete collection of these stamps in our next Public Auction. It gets posted today.