Frontier is another budget carrier which flies 737s to Denver with a stop in Omaha. The problem is there is only one late night arrival and one early morning departure. American Eagle is the commuter service for American and the airline we use the most. They fly 5 flights daily to Chicago O Hare and back with a flight every 4 hours or so. Northwest flies commuter service from Detroit or Minneapolis.
Aircraft are usually medium sized but the flights usually have brief stops in other cities.
It is the airline we are least familiar with but friends indicate it is generally reliable. And just to be complete, Amtrak goes through the middle of town in-between Chicago and St. Louis several times a day.