I agree with most others...Tom Hargrove has my vote. I feel going into a flyshop is not so much having some shopping to do, but more be able to shoot the breeze with some friendly folks.
Having said that, for the St. Charles, St. Peters, O'Fallon folks...when I'm in town (St. Charles), if I need something quick, and don't feel like the doing the roadtrip to Hargrove's, I'll run into Cabela's or BassPro. As some folks said already, the inventory is not the greatest but if I need something quick it's usually something like tippet and that kind of stuff usually isn't a problem at those places.
Mike-