I stayed at the Drury on a family trip. Great Hotel, right by the arch. I’d go there again. Lots of beggers though, I got shook down three times.
The Union Station area is good and the best deals on Hotels if you have a week long stay might be Priceline for the ST. Louis area. Go to this site and you can see what the rooms are going for in that area. If your not going to change plans. Book it now and you will get a cheap rate. The Hyatt Union Station is going to be converted to a Marriott and so the rates will fall while its in transition.
http://biddingfortravel.yuku.com/forums/61/t/Missouri-St-Louis.html