Last time a left handed catcher played in the major leagues:

1989
Benny DiStefano of Pittsburgh caught three games for the Pirates in 1989, the sixth left-handed catcher since 1900. The others: Mike Squires, Chicago White Sox, two games, 1980; Dale Long, Cubs, two games, 1958; Tom Doran, 46 games for the Boston Red Sox and Detroit from 1904-06; Joe Wall, seven games, New York Giants and Brooklyn, 1901-02; and Jack Clements, Boston Braves, 10 games, 1900.
Source: Cleveland Plain Dealer, 11/8/2001

 
   
  First left-handed quarterback to be voted into the NFL Hall of Fame:

Steve Young
Young passed for 33,124 yards and 232 touchdowns in a 15-year NFL career.
Source: Associated Press, 11/20/2005

 
   
  First left-handed golfer to win the Masters:

Mike Weir
In 2003, Weir won a sudden-death playoff against Len Mattiace to become the first lefty to win the Masters.
Source: Augusta Chronicle, 4/9/2006

 
   
  First left-handed heavyweight boxing champ:

Michael Moorer
On April 22, 1994, southpaw Michael Moorer beat Evander Holyfield to win the IBF and WBA heavyweight titles.
Source: Houston Chronicle, 4/22/2006