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.
Of the 1.9 million sets issued, it is likely that at least 90%-95% were used as postage and discarded, leaving perhaps 100,000 to 200,000 sets remaining. The stamps were issued in sheets of 100, with one plate block of 8 and one center line block per sheet, of which perhaps 1,000 to 2,000 of each remain. The plate blocks of 8 are pricey (CV of 180.-/275.-NH for #620, and 450.-/750.- NH for #621), but the center line blocks are overlooked and undervalued (CVs of $16.-/22.50 NH for #620, and 70.-/125.- NH for #621).
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.