The Boulton is probably the most popular watch in Hamilton's entire history. It first came out in 1940 and aside from the enforced shutdown of production during WWII it stayed in the catalog up to 1969. (The dial was modernized in 1960 and it was dubbed the "Boulton II".)
When Hamilton decided to launch a series of reproductions of classic designs in 1982, the Boulton was the first watch chosen. Those first replicas had mechanical movements, but they soon came out with a quartz version and variations have stayed in the line ever since. That adds up to just about 50 years that this classic design has been produced.
How many consumer goods can you think of that have designs so incomparable that they are as popular in 2008 as in 1940?