Kennedy, 30, who played seven seasons for the American League Angels, signed a three-year deal with the Cardinals, who were helped to the championship this season by World Series MVP Eckstein.
Kennedy, a career .280 hitter with 52 homers and 369 runs batted in, batted .273 with four homers, 55 RBIs and 16 stolen bases last season for Los Angeles.
He played four seasons alongside shortstop Eckstein while with the Angels.
Trachsel joins Orioles
St Louis also signed right-handed pitcher Kip Wells, 29.
Wells, who missed much of 2006 with a blood clot in his shoulder, was 2-5 with a 6.50 earned run average in nine starts.
He threw 44.3 innings last season with the Pittsburgh Pirates and Texas Rangers.
Brewers sign Suppan in record deal
McCarthy joins White Sox