Left Field: Lou Brock
Brock only made the postseason three times in his 16 seasons with the Cardinals, but he made the most of it. What seemed to be a lopsided trade at first with the Cubs when the Cards shipped 20-game-winning pitcher Ernie Broglio for the unproven Brock, but it turned out to pay huge dividends for the Cardinals, right away.
In 1964 when the Cardinals acquired Brock, he helped them pull off a remarkable late-season run to steal the division away from the Phillies and Reds to propel themselves into the World Series to take on the Yankees. He helped the Cardinals defeat the Yankees in seven games, as Brock hit .300 in the series.
Three years later, Brock upped his game in his second World Series, this time against Boston. In Game 1 he went 4 for 4 at the plate and stole two bases en route to a Game 1 road win, and he had at least two hits in all four wins in the series, helping the Cards win their second championship in four years.
He made the World Series again the following year and again he improved from his previous postseason appearance, including a three-hit, three-steal game in Game 3, and a three-hit, four RBI game in Game 4 where he fell just a single shy of the cycle. Despite his exceptional hitting in that series, the Cardinals fell to the Tigers in seven games.
Brock's 14 career steals in the postseason were the most at the time of his retirement and is still tied for eight in MLB history.
Honorable mentions: Joe Medwick, Matt Holliday, Lonnie Smith, Allen Craig
Center Field: Jim Edmonds
"Jimmy Ballgame" shined in the postseason during his time in St. Louis. The Cardinals traded for Edmonds in the 1999 off-season after he played several seasons with the Angels, he failed to reach the playoffs with Anaheim (he played in a one-game tiebreaker in 1995 that counted as a regular season game).
He didn't have to wait long to play in the postseason, as the Cardinals won their division in his first season, and they went on to sweep the Braves who were in the middle of their 15 straight seasons of making the playoffs stretch. Edmonds hit .571 with two HR and seven RBI in the three-game series.
Edmonds had a run of hitting at least one home run in seven straight postseason series, capped off by a season-saving walk-off home run in Game 6 of the 2004 NLCS against the Astros.
In 64 career playoff games, Edmonds hit .274 with 13 home runs, 42 RBI (41 with the Cardinals), and an .874 OPS.
Honorable mentions: Colby Rasmus, Willie McGee, Harry Walker
Right Field: Carlos Beltran
There were a lot of candidates for this spot, but it's hard for me to argue with somebody with the postseason resume that Beltran has, even though only two of those years were in St. Louis.
Before Beltran became a postseason hero for the Cardinals, he was torturing the Cardinals in the postseason. With the Astros in the 2004 NLCS and with the Mets in the 2006 NLCS, Beltran hit .353 with seven home runs, nine RBI, five stolen bases, and 12 walks in 14 games. However both times the Cardinals were able to prevail and prevent Beltran from making it to the World Series.
Beltran didn't play in the playoffs again until, ironically, with the Cardinals, when he signed as a free agent prior to the 2012 season. His stellar play in October carried over with the Cardinals, hitting .357 with three homers and six RBIs in 12 games, but for the third time in his career, he fell one game short of reaching the Fall Classic.
2013 was another strong playoff for Beltran headlined by his play in Game 1 of the NLCS against the Dodgers. He drove in both Cardinal runs before the game went into extra innings, and then he contributed defensively. In the top of the 10th with Mark Ellis on third, Michael Young hit a fly ball to right center, Jon Jay intentionally let the stronger arm in Beltran catch the ball, and he delivered a perfect throw to Yadier Molina to nab the go-ahead run at the plate. Later on in the extra innings, Beltran got the walk-off hit off Kenley Jansen to win Game 1.
That was finally the year where Beltran would get to the World Series, and he would have to wait until his final season in 2017 to win a title, albeit controversially.
Honorable mentions: Lance Berkman, Enos Slaughter, Jose Martinez, Tito Landrum, Ryan Ludwick
It's now time to see who the battery would be, and the bullpen