Ryan Howard
Lou Gehrig led the Major Leagues in home runs in 1936 with 49
The Chicago White Sox led the majors in Home Runs with 235.
Barry Bonds and Juan Gonzalez each hit 46
Albert Belle of the Cleveland Indians hit 50 home runs in 1995 to lead MLB.
The American League leader in home runs for the 2006 season was David Ortiz of the Boston Red Sox with 54.
Albert Pujols led the MLB with 47 home runs in 2009. He was followed by Prince Fielder (46) and Ryan Howard (45)
Ryan Howard of the Phillies hit 58 homeruns in 2006.
In 1973 Willie Stargell led the National League in home runs with 44, and Reggie Jackson led the American Legue with 32.
Sammy Sosa led MLB in home runs in 2000 with 50.
Mark McGwire. In 1997, McGwire's 58 home runs led MLB. He hit 34 for Oakland, was traded to St. Louis on July 31, and hit another 24 for the Cardinals. So while he didn't lead either league in HRs, he led the entire MLB in HRs.
In 2005, Andruw Jones, then with the Atlanta Braves, led all Major Leaguers with 51 home runs. He now plays for the Texas Rangers.
Rogers Hornsby led the Major Leagues in home runs in 1925 with 39 home runs for St. Louis.