Not much left out here anymore...
The one that I frequent the most is Baseball Plus. The owner Mark is a good guy and has been involved in the hobby a long time. He sells on ebay under the ID markplus. If you look there that should give you an idea of what he has to offer at his store. Mainly Modern wax & vintage singles (50s,60s & 70s).
Baseball Plus
Address: 346 Mid Rivers Mall Dr, St Peters, MO 63376
Phone: (636) 970-7088
The only other shop I have even been to (that still exist) is 1,000,000 Baseball Cards. They have some pre war stuff there. If I lived closer I would probably frequent their shop more.
Address: 14560 Manchester Rd #23, Ballwin, MO 63011
Phone: (636) 527-4424
http://www.onemillionbaseballcards.com
RBICru7 Sports cards has mostly favorable reviews but I have no personal experience with them.
Address: 1030 Rue St Francois, Florissant, MO 63031
Phone: (314) 395-9001
Depending when you are in town there is a pretty good monthly card show ran out of Orlando Gardens in South County. Check out their website for more info:
http://stlsportscollectors.com/
Have a good trip!
Scott