The Phillies finally got their first HBP of the postseaon last night, when Eric Bruntlett got hit by a pitch to lead off the 9th inning. He came around to score the winning run, making that the first time in World Series history that the walk-off winning run was scored by someone who reached base on an HBP. It's very interesting that the Phillies first HBP of the 2008 postseason was recorded not by the guy who got hit 27 times in the regular season - but by the guy who used to be play for the Astros alongside the modern era HBP king, Craig Biggio.
The last time the go-ahead run was scored by a plunked batter in a World Series game was game 6 of the 1992 series, when Charlie Leibrant hit Devon White in the top of the 11th inning. He then gave up a Roberto Alomar single and a Dave Winfield double, which drove in White as the go ahead run, and Alomar for a needed insurance run. Atlanta got one back in the bottom of the inning, so White's run wasn't the ultimate difference maker, but it was a clutch HBP.
In game 2 of the 1974 World Series, Sal Bando got plunked by Don Sutton to lead off the bottom of the 9th for the A's, and scored on a Reggie Jackson double, but Bando's run left the A's still down 3-2, and the rest of the team could not continue the rally. That was the last time a batter got hit to lead of the 9th inning or later, and scored a run, before last night.
In game 4 of the 1957 World Series, the Milwaukee Braves entered the bottom of the 10th inning, trailing 5-4. Tommy Byrne hit lead-off pinch hitter Nippy Jones. Jones was replaced by pinch runnner Felix Mantilla who move to second base on a Red Schoendienst sacrifice bunt, and then scored on a Johnny Logan double to tie the game. Eddie Mathews then won the game with a two-run homer, but it was Nippy Jones' HBP that started the rally.
In game 1 of the 1907 World Series, Harry Steinfeldt got hit by a Bill Donovan pitch in the 9th inning, and came around to score the tying run. That game went another 3 innings but ended in a tie (back when that sort of thing was allowed).
4 other batters got hit by a pitch in the 9th inning or later, and scored a run, but none of those runs was integral to the outcome of the game. In 1979, Bill Robinson took a plunk with the bases loaded in the top of the 9th inning of World Series game 7, but that just extend the Pirates lead to 4-1 and sealed their victory.