William H. Gross was a famous stamp collector, and this 2 cents Hawaiian Missionary stamp was the most valuable stamp in his collection. The stamp, dating back to 1851, went for $619,500 at a ...

with the rarest being one of two known one-cent "Z" Grill stamps from 1868. If sold for its estimate of $4 to $5 million, the ultra-rare collectible would become the most valuable American postage ...