Walking distance from the Arch. Hmm.
Headed south, you'll first hit the Broadway Oyster Bar. Good fare, live music. A little further on, you'll hit 4 Hands. Pretty sizable local brewery. A little further, you'll find International Tap House. Lots of beers, 'industrial chic'.
I'm a big fan of Civil Life's beers, but they're outside walking distance. Nice easy drinking renditions of classic styles.