I was looking at the list of players who have hit 2 HR in the same inning today, for a post in another thread, and found some Curious Facts related to that.
The feat has been accomplished 59 times in history.
Brothers Aaron and Bret Boone did it about three months apart in 2002.
In the game where Bret Boone accomplished the feat, teammate Mike Cameron did, too...in the same inning.
It looks like three players have done it twice: Willie McCovey, Andre Dawson, and...Jeff King
When Fernando Tatis did it, the home runs were both Grand Slams; the only time in history that has happened.