Honorable Mention- Lee Smith RP
More people probably remember Lee Smith for his time with the Cubs over his brief stint with the Cardinals. However, some of Smith's better seasons took place during his time in St. Louis. In 1991 Smith recorded a total of 47 saves which set the National League record at the time. I first got to watch Smith pitch with the Cubs during the mid 1980s when the Cubs games were on WGN every afternoon. Whether they were playing the Cardinals or not, the daytime Cubs games were always a good way to pass sometime during the summers. I would be more inclined to rank Lee Smith on this list if it weren't for his partial 1993 with the Cardinals. It was brutal and there were a lot of blown saves/leads.
5. Bob Tewksbury SP
Tewksbury may not be a name that some know, or remember, but he did play for both teams during his career. His Cubs career was all of 8 games after the right-handed starting pitcher joined the baby bears in a trade with the Yankees for pitcher Steve Trout. Most of Tewksbury's Cubs career actually took place in Triple A. The Cardinals signed Bob Tewksbury during December of 1988. He spent some time in Triple A with the Cardinals too before he landed a gig in the team's starting rotation during the 1990 season. Playing for the early/mid 1990s Cardinals meant a whole lot of losing, but Tewksbury was a good pitcher. Not just compared to the rest of the rotation, but actual good pitchers like Greg Maddux. His best season with the Cardinals, and his career, took place in 1992 when he went 16-5, had an ERA+ of 158, and a WAR of 6.5. Tewks finished 3rd in the National League Cy Young voting that season. He bounced around to a few teams after he left the Cardinals, always a fan even if he wasn't always the best pitcher.
4. So Taguchi OF
Taguchi played in St. Louis for a total of 6 years and in Chicago for a single season. He was not a regular starter for either team, but he was a really easy player to cheer on. Taguchi's main contribution during his eight year career in the U.S. was as a defense first fourth outfielder. The highlight of his Cardinals career came in 2006 when he helped the Cardinals advance to the World Series with a key home run off of Billy Wagner during Game 2 of the NLCS. So Taguchi ended up on the Cubs in 2009 after winning a second World Series with the Phillies in 2008. He actually spent the majority of the year with the Triple A Iowa Cubs, but was called up for a few games at the end of the season.
3. Shawon Dunston SS
Another 1980s Cubs player who I first saw on WGN watching baseball during summer break. Everyone who watched a Cubs game in the 1980s knew about the Shawon-O-Meter, a sign which showed the shortstop's batting average. It always made an appearance at some point during every telecast. Dunston was a very good shortstop for the Cubs for a dozen years, but spent the latter part of his career bouncing around the league as a bench player. He appeared for the Cardinals for two seasons in 1999 and 2000. Dunston was most noted for having a rifle arm, but too me, was just an overall exciting player who had a little bit of everything in his game.
2. Jon Jay OF
Jay was a long time start for the Cardinals. Never a star player, Jay just went out and played everyday the best he could. Much of his time with the Cardinals was overshadowed by players like Albert Pujols and Yadier Molina, but he still spent the better part of 6 seasons patrolling center field in Busch Stadium and getting on base at the top of the line-up. He's the only active player on this last, and is in his first season with the Cubs, but Jay is one of the former Cardinals player I always check out in the box scores every morning. His role has been a little bit more limited with the Cubs, but he's still been a positive contributor for the Baby Bears.
1. Jim Edmonds OF
There were so many great moments that Edmonds had with the Cardinals during his eight years with the team. It's hard to remember him as a Cub, but he spent one season on the north side of Chicago. After the Cardinals traded their center fielder to the Padres for David Freese, he fizzled and was released. He signed with the Cubs and actually had a good year for the team in 2008 posting an OPS of .937 and 19 home runs in just 85 games. The Cardinals were not very good that year and the Cubs ended up in the playoffs, so this one hurt a little bit more than the others. Still really like Jim Edmonds even if he spent some time with the Cubs.