C. Lee said:
Hate to do this again big guy.....in Superman IV, as he is deciding what to do about the nuclear weapons...Lois comes to Clark's apartment to go to the "press awards" dinner......he walks her out on his balcony (dressed as Clark) and jumps off of it with her....he then changes to Superman, and they fly around the world looking at things....they come back to his apartment....he says "You don't even know my name"...she says "Kal-El....I remember everything.".......he smiles and says "never put one above the rest" (or something like that)....he kisses her again....and once again she loses her memory.
They used the memory erasing kiss in 2 of the movies.