Only Ryan Dempster and Kerry Wood are meaningful contributors eligible for free agency (sorry Jim Edmonds, Bob Howry, and Henry Blanco.) Given the market (read: insane money) thrown at starters and closers I'm not so sure either will return, although given their special circumstances it's more likely than, say, Francisco Rodriguez returning to the Angels. Wood in particular is probably a 95% guarantee to stay. Dempster on the other hand might test the market, given his unlikely season he could be looking at a handsome payday from the losers on Derek Lowe, A.J. Burnett, and CC Sabathia.
The Cubs' needs include center and right field. It appears Kosuke Fukudome's average season will earn him a spot in the proverbial wine cellar. Best-case scenario for the Cubs would include landing an excellent defensive center fielder and letting their abundance of iffy outfielders (see: Fukudome, Reed Johnson, Micah Hoffpauir, Felix Pie, ect) battle for right field and the bench.
Interesting that scenario could have the Cubs sliding Fukudome to center (their best outfield defender) where his offense would not be quite as exposed and his defense would be better than the aging combination of Edmonds and Johnson.
Shortstop is a seemingly simple upgrade for a team with financial resources so rich. Ideally, the Cubs would renew their interest in Rafael Furcal from a few seasons ago and upgrade offensively and defensively over Ryan Theriot. Heck even Orlando Cabrera would work, assuming they would deal with his antics.
The good news for the Cubs is they will remain in the National League Central, a division almost certain for one team to lose some of its luster (Milwaukee) and three teams likely not contending next season (Houston, Cincinnati, Pittsburgh). That leaves the Cubs, Cardinals, and whatever the Brewers can retain fighting for the division title.