In 1925, the U.S. issued a set of two stamps celebrating the 100th Anniversary of the arrival of the sloop "Restaurationen" with the first group of immigrants from Norway (Scott #620-21). About 9.1 million of #620 and 1.9 million of #621 were issued, and Scott '13 prices the unused set at $13.25 ($26.50 for NH).
These stamps have appeal to both Scandinavian-American collectors and collectors of Transportation/Ship topicals. The printing quantities were higher than for most of the stamps that I normally recommend; however, I am not recommending purchase of the basic set.
While it's certainly true that plate blocks are more popular than center line blocks, I feel that the center line blocks of this issue, which sell for a relatively minor premium over the price of the basic stamps, are a much greater bargain.