I have two favorites.
International Tap House (one location in Soulard, and one in Chesterfield)
This place is great for their huge beer selection, and the owner, Brad, is a nice guy. Also, though they don't serve food, you can bring food in order have it delivered, which is an advantage, in my opinion.
Just north of Sarah and Forest Park Parkway between Grand and Kingshighway.
They have a good beer selection including several great draughts. Their food is quite good, and they have a 'farm fresh' menu that starts on Thursday and lasts as long as it lasts. It's based on ingredients they receive fresh from a local farm that day. The bar is dimly lit with lots of dark wood. Great atmosphere.
Oh, and I suppose I have to mention all the staff wear kilts.