Fiorella's Jack Stack in the freight district (across from Union Station, right next to downtown)...it's a very nice BBQ place and they have great prime rib...I've never had anything there I didn't like.
There are quite a few places to eat in the P&L, I personally like Gordon Biersch and the Bristol (seafood)...
I'm telling you though, Jack Stack is the place to go...I've taken numerous out of towners there and they all loved it...and get the Crown Prime Ribs...they're 3 huge ribs that look like dinosaur bones...awesome...