Big Sky has been awarded three EAS cities for that area: Cape Girardeau, MO, Jackson, TN, and Owensboro, KY. Great Lakes has also been awarded three in that area: Burlington, IA, Fort Leonard Wood, MO, and Marion/Herrin, IL. Here's the FAA document awarding both carriers the cities:

http://dmses.dot.gov/docimages/pdf100/458711_web.pdf

Other airlines off the top of my head based in St. Louis:

American
Trans States
GoJet (I think)