The 1906 Chicago Cubs have the best winning percentage for a season with .763. The Cubs 1906 record was 116-36.
The Los Angeles Dodgers
The all time MLB record for losses was set by the 1899 Cleveland Spiders with a record of 20-134.
116 wins Seattle Mariners
Who has the best ERA for a MLB season
2001 Seattle Mariners they went 116-46.
The Chicago Cubs at the moment (6-6-08)
Owen Wilson, an outfielder for the Pirates and Cardinals between 1908-1916, holds the single season record for triples with 36 in 1912.
In the 2009 season, Mark Reynolds struckout 223 times which was an new MLB record. He broke the old record of 204 set by ... Mark Reynolds in 2008 season. He is the only player in MLB history to have struckout 200+ times in a season.
The New York Yankees (62-15) in 1933
The most games lost in a season by an MLB team is 134 by the 1899 Cleveland Spiders. The Spiders record that season was 20-134.