Brian McCann just did it a couple of days ago (pinch hitting in the 9th). I asked HR expert David Vincent (of SABR and Retrosheet) "Do you know how many times a player has hit a game tying HR in the 9th inning and then won the game with a HR in extra innings?" Here is the list he sent me, used with his permission. The hot link will take you to the boxscore and/or play-by-play for the game, as it does for McCann.
08/27/1949 Jeff Heath
04/29/1985 Donnie Scott
04/08/1986 Jim Presley
05/08/1990 Andre Dawson
06/10/1998 Robin Ventura
04/05/1999 Raul Mondesi
04/11/2000 Ed Sprague
06/14/2002 Aaron Boone
08/27/2002 Joe Crede
08/20/2004 Adrian Beltre
Jeff Heath also pinched-hit in the 9th inning of his game. His winner was in the 10th inning and both were off of Ewell Blackwell, who was pitching in relief. It is interesting that this was only done once before 1985 and has been done 10 times since (including McCann). Why so many recently while there were so few before?
In the Ventura game, the Sox trailed the Cardinals at home by 4 runs in the bottom of the 9th with 2 outs and no one on base. After Albert Belle hit a 3-run HR, Ventura hit his tying HR. Then he hit a 2-run HR in the 11th.
Presley's was opening day and his game winner was a grand slam. Mondesi's was opening day as well. Beltre drove in all the Dodger runs in his game (they won 3-2). Crede's game winner was also a grand slam and it was on the anniversary of Jeff Heath's game. Crede drove in 7 of the 8 runs for the White Sox that day.
Update 5-20: At Baseball Musings, commentor npbcardguy mentions a game when Mike Young of the Orioles hit a game tying HR in the bottom of the 10th and a winner in the 12th. Click here to see the boxscore and play-by-play. Does anyone know of any other games like that?
David Vincent found these other occurrences:
05/17/1971 Ralph Garr
06/14/1963 Willie Kirkland