My favorite St. Louis brewery is Schlafly; their Pale Ale is great for any occasion. Their seasonals (esp last year's Pumpkin Ale) are typically top-notch. They have yet to disappoint me.
There are a LOT of craft breweries in the area, many new, within the last 2-3 years. If you're visiting, make time to visit places like Urban Chestnut, Morgan Street Brewery, Square One, 6-Row, and the Schlafly Taproom (really good food, there, & they'll give you a really good tour if you ask nice enough). There are more, many much more, but I can't think of them off the top of my cranium.
Cheers from the Lou.