St. Louis is what I consider very "under-groceried" -- especially since Kroger left the area in 1986 and Loblaws' sole U.S. operation (National Markets) ceased to exist in the 90's.
With that said, you have the following "major players":
Schnucks - the 800-pound gorilla that bulked-up after Kroger's departure (and they bought/merged with National in 1995, and got a whole lot bigger -- which raised many eyebrows in the Federal Trade Commission). Locations nearly everywhere in/around St. Louis, as well as other midwest states.
Shop n' Save - the local brand for SuperValu (Jewel-Osco, Acme, and others) - 42 locations in the metro area.
Dierbergs - the smallest of the three -- generally considered more "upscale" and in format/layout/pricetag compares to stores such as Publix and Wegmans. - 23 locations in the metro area.
In addition to those three,
Walmart has been emerging over the past few years by rebuilding their longtime general merchandise stores into supercenters, and Target completed a remodeling "blitz" last year which added small fresh grocery sections to all of their local stores (both WM and Target have been part of the St. Louis retail landscape since the late 60's/early 70's).
Interestingly-enough, none of the "locals" have club card promotions like their counterparts in other regions of the U.S.
Aldi is also popping-up in certain neighborhoods, albeit, in much smaller numbers than the rest of the pack...
Caveat: I am speaking only of those stores the general public can shop at (no warehouse clubs or military commissaries, both of which are available in the area)