OMG!

I forgot Soulard Farmer's Market, the whole Soulard area, Pevely Flea Market (hour drive to buy other people's crap)... Argh! I'm sure I'll think of more...
Downtown, including Union Station, the train depot turned shopping mall, get some Hodges Chili if you visit... Look at all the people wearing red for the Cardinals baseball game, I'm sure there will be one during your stay... There's just so much to do. How long were you planning on being here?