Walk-off Grand Slams are the most majestic plays in baseball. I have never seen one in person and doubt I ever will. On May 13th, 2012, Mother's Day, Joey Votto smashed a Grand Slam in the bottom of the 9th to secure a win over the 21-13 Washington Nationals.
While searching for the above 2012 Opening Day Superstar Celebrations Votto card I ran across a 2011 Diamond Duo. The duo being Votto and Hamilton. One of which had four home runs in one game just the other week, and the other three home runs, one of which was a grand slam.