I can recommend two favorites. The first is The Ink Spot in Kirkwood. Julie has an awesome selection of stamps, and she carries a big assortment of amuse stamps as well! Great displays, too! I hear she's having an event for The Saltbox Studio on March 15th also! Here's the link:
http://www.inkspotofnatalie.com/
My other favorite is Rock Paper Scissors in historic St. Charles. Corey has an awesome shop! Lots of fabulous papers and accessories, as well as fun stamps. Here's the link to Corey's blog:
http://rockpaperscissorsblog.blogspot.com/
If you go to St. Charles, make a day of it! It's a fun place to shop, eat, and explore.
Have a great time! I'll be saying goodbye to my St. Louis home this month, but it's been a fun place to live. Enjoy!