Now granted it is only mid-December and there is still plenty of time left for teams to improve upon their current roster, but I gotta say so far that I don't see any of our now 4 remaining division mates as being notably improved.
Brewers - For a team that has often been very active in past offeasons, I'm really surprised so far by their inaction. Their rotation is Gallardo and a series of question marks. I could see them going after Kyle Lohse or Edwin Jackson, but I'm not sure if they are willing to spend the money they will be looking for. I see them more so looking at guys like Brett Myers and Carl Pavano and perhaps trying for another Greinke/Marcum type trade. They have some sluggers, but right now the feckless Carlos Gomez is penciled in at CF and it seems likely that Jean Segura could have growing pains at SS.
Pirates - They upgraded their catcher position and that's it. Their rotation is a series of question marks after A.J. Burnett and Wandy Rodriguez. They are basically the same team they were that lost all those games in August/September just with a better catcher. Can't write them off completely, but at some point they are going to have to actually prove they can have a winning season.
Cubs - Epstein has done some nice patchwork with the rotation, acquiring solid starters like Scott Feldman and Scott Baker to go along with Matt Garza (who could still be traded) and Jeff Samardzija. Staying healthy is not the strong suit of these guys though. Like the Pirates, their lineup so far is basically the same barring a Soriano trade. It seems unlikely they will lose 100 games again this year but it's very, very hard to see them as a threat to the division right now.
Cardinals - So far, traded Skip Schumaker and signed Randy Choate and Ty Wigginton. Obviously their lineup is set and their rotation is pretty much as well, though losing Lohse will hurt and Wainwright/Carpenter/Garcia each had injury/effectiveness problems in 2012. Still, they remain the biggest threat to a Red October.
This is all just one man's opinion though. Feel free to chime in.