OK, here's a pretty well-worn example that I'm sure must have been already posted elsewhere in the CCF boards, but I'll add it here too--the cover of Adventure #247, which has been homaged numerous times.
The first such recycle--its use on Superman #147-- is a great example of the internal consistency/mythology within the Weisinger books and illustrates an editorial awareness of/nod to the readership base. The Superman cover's source was obviously meant to be recognized--an aha! moment for the readers. Curt Swan was the artist for both the 1958 Adventure cover and the 1961 Superman cover.