Lots of talk on who to trade.  Here's my take.  First off, they won't be able to trade everyone.  No one does so we don't have to worry about a whole team of AAA guys.  

The bullpen guys (Williamson, Dempster, Eyre and Howry).  Every contender needs bullpen help.  These guys are probably the easiest to move.  The Cubs aren't winning this year or next so they are expendable.  Trade as many as you can for prospects.  Guzman, Aardsma and Hill can backfill as needed.  Whatever they do, Guzman needs to pitch somewhere!

Walker.  He's gone after this season so he should be traded first.  Let Fontenot play if you move him and no I don't think Fontenot will be the starter next year.  Just see what he can do.

Maddux.  He's earned the right to say what he wants.  If he wants to be traded, trade him for whatever you can get which I don't expect is too much.

Pierre and Jones.  These two should not be given away.  They could return next year and start again.  However, if someone makes a decent offer, take it.

Barrett.   I don't think there is much market for him so they might as well hang on to him for this year.   Consider someone else for next year.  

Ramirez.  I don't like his attitude but he is a solid hitter.  No need to trade him unless you get a couple of Grade A prospects.  

Nevin, Mabry, Perez, Rusch.  These guys have no value.  Get a few hot dogs if can.

Bynum, Pagan.  These guys have little trade value.  No you can't package them up with Hill and Dopirak for Cabrera.  Play them.  Neither look like starting material but maybe one could be a 4th OFer in the future.

A final point, if they can find a scrub starting pitcher, get them and give Marshall and Marmol some AAA time.  Marshall has a 59/42 K/BB ratio in 86 innings.  He is not ready for the majors.  I like him, don't ruin him.