I was perusing the Chicago blog scene and came across this interactive map at the Chicagoist site. The map allows you to select an "L" stop for a drop down list of amenities. Really cool. I'd be wary of the updating, but gives you a great sense of what type of neighborhood straddles each stop.
It's like that guy on PBS who travels Chicago by the "L"... expect you don't have to watch the whole part about chicago's meat packing history to find a bar in the West Loop. Just click away.