The Hyatt Regency is a beautiful hotel with a beautiful view. Depending on what room you're in, you'll be able to see the Arch right out of your window. The rooms were clean, the staff was friendly, and the location downtown was great.
My only real complaint is the price, but I guess you get what you pay for. The $50 a night valet only parking was also a pain, with long lines, but I guess it beats parking on the street downtown.