It really should come as no shock to anyone that Mark DeRosa has hit seven homers in his first 19 games as a Cardinal, or that Matt Holliday, in his first 10 games wearing red cleats, is an absurd 20-for-37 with three jacks and 10 ribbies. It's almost a foregone conclusion: if you get traded to the St. Louis Cardinals during the summer, you instantly become The Man. In the past few years the Cards have had a rather ridiculous return on their investments acquired near the deadlines. For instance ...
1997: The Cards get Mark McGwire from the A's. He homers in his first appearance at Busch, and finishes the year with 24 HR in 51 games, an even more aggressive pace than the next year, when he broke Maris' record with 70.
2000: In his final season, Will Clark gets traded to St. Louis from the Orioles. He hits a home run in each of his first four starts, and over 51 games hits .345 with a 1.081 OPS, 12 HR, and 42 RBI as the Cards make the playoffs.
2002: After wearing out his welcome in Philadelphia, Scott Rolen hits 14 HR in 55 games with a .915 OPS for the Cards. They also acquire Chuck Finley, who turned his season around (7-4, 3.80 with St. Louis) after struggling mightily in Cleveland.
2004: The Cardinals trade for Larry Walker, and the former Rockie his 11 HR in 44 games with a .953 OPS. Not bad. The he drills six more homers in the playoffs as St. Louis made a World Series run.
2006: This one is the most improbable of all. Jeff Weaver was having a nightmare season with the Angels (3-10, 6.29 ERA) when he was traded to the Cardinals. He didn't fare much better (5.18 ERA in 15 starts) as St. Louis backed into the playoffs. But in five postseason starts, Weaver ripped off a 2.43 ERA and was the winning pitcher in Game 5 as they won the World Series.