Also the meetings between Superboy and Superman, I belive they have met twice, one was in the Superman in the 70's TPB and the other in DC Comics Presents.
I'm not sure if this is one of those two, but there was a multi-part crossover between
Superboy and one of the
Superman titles where Superboy's mind came to the future to inhabit Superman's body, while Superman's mind went to the past to inhabit Superboy's body. They had to work together across the time-stream to get the trouble straightened out.