In the 1971 All-Star game, Reggie Jackson ALMOST cleared the wall, but it hit a metal structure on top of the roof. I suspect a pretty fair number of us who were alive at the time remember that monumental home run off Doc Ellis.
Cecil Fielder, Harmon Killebrew and Frank Howard all cleared the left-field wall - which is a much harder accomplishment.
Babe Ruth did hit one in July, 1921 when the "Old Ballpark" was known as Navin Field. I suspect that because he was a left-handed batter, his cleared the RF wall.
Certainly, hitting a slow pitched softball is a totally different dynamic so Mike's out-of-the-park blast (fair or foul) is quite an amazing feat. One other thing about Mike - everyone who calls him a great ambassador for the game is spot on.