Superman #300 (June 1976) is one of my favorite comics that I remember originally getting when it first came out. I lost the issue somehow but I bought a copy again years later for ten times the original cost and in very used condition. "Superman 2001" is a Just Imagine story where little Kal-El lands on Earth in the present day and starts as Superman in 2001.
Note: I deleted the t-shirt and Amazon link.