Superboy in "Journey to the Moon"
When Clark accidentally takes a trip to the moon with an absent-minded professor, the professor discovers his secret identity. But when they return to Earth the professor can't remember which boy in Smallville is the Boy of Steel.
Green Arrow in "Untold Arrow Tales"
Aquaman in "The Sleuth of the Sea"
Aquaman meets Phineas Pike, the Sea Sleuth.
Johnny Quick in "The Man Who Hated Water"