Nearly every player on the Cubs is a potential trade candidate so talking about each one would be exhaustive and pointless. Luis Valbuena is a trade candidate though why any team would trade for him, I don't know. It's not like there was a line of teams wanting to sign him after he was DFA'd and he's not been very good so it's safe say that he's a candidate, but not a very good one. And not worth any more discussion. Same goes for others like him. You know who they are. They litter the Cubs roster.
Matt Garza is going to be out of action until after the deadline with an arm-related injury so take him off the market. It's possible a team would still want to acquire him, but not at all likely any team would be willing to give up what they may have before considering the injury. As a result, it's safe to say he'll be a Cub on August 1st. There is the waiver deadline at the end of August so he could still be traded in August, but the Cubs would lack any leverage in negotiations. I wouldn't put much money on him staying put all season, but I feel confident saying he's probably going to be a Cub when the season ends.
At that point the team can revisit trading him. Theo and Hoyer can also slap each other in the face a few times between now and then for not trading him last offseason. He had more value last offseason with 2 full years remaining prior to being eligible to file for free agency than he'd have had four months later at the deadline. Not to mention, there's always a decent possibility a pitcher will get injured. Considering Garza was coming off what was arguably the best season in his career, one should have expected he'd regress, which would then of course lower his value. Garza should have been traded last offseason if the team had interest in doing it and they clearly did. They worked through much of the offseason talking to teams about Garza and those talks continued as the trade deadline approached this year.
Instead of acquiring the quality prospects the Cubs could have last offseason, they're stuck with a player who will receive roughly $12-13 million next year and be projected for no more than 3 WAR. He has very little surplus trade value now.
To the Cubs credit, they worked out a favorable deal for the team by trading Ryan Dempster to the Braves for Randall Delgado. Dempster would of course decline the trade. I'm unsure if he ever actually declined it, but he never agreed to it, which is the same thing. The deal went down the drain along with any leverage the Cubs had. They're now stuck negotiating with the Dodgers who know they have the leverage and other options still available so they're not going to give up what the Cubs want.
Braves GM Frank Wren has said they've moved on and the deal is off the table, but it's possible the Cubs could go back to him with Dempster's approval and receive the same prospect in return. The chances of this become slimmer each day, but it's what Theo and Jed are hoping for. Whether or not it proves to be false hope remains to be seen.
Garza entered the season as the most likely trade candidate and Dempster joined him with his especially strong first half. Aside from those two the Cubs lack any trade candidates who are going to help out the organization beyond a marginal improvement. There was the possibility that Geovany Soto could rebound, but that hasn't happened. He's split time behind the plate and not performed well doing it. Catchers are valuable and although Soto is making more than you'd hope for someone who is performing as he is, it wouldn't surprise me to see a contender looking for a better backup in the next few days.
Ian Stewart is out for the season. The Cubs had hoped he'd turn his career around and become a contributor for the Cubs. At worst they were hoping he'd improve somewhat and become corner infield trade candidate. That didn't happen and it's probable that Josh Vitters will be taking over at the hot corner next season so Stewart's days as a Cub are probably over.
Jeff Baker has some value, but not all that much. He can hit lefties well and play multiple positions. Every year these types of players are acquired and every year teams get C prospects in return.
Carlos Marmol entered the season as an interesting player if things went right. He was coming off a down season, but the guy has potential nobody can deny. He also has some of the worst control anyone has ever seen at the MLB level. This year the control got the better of him as he's walking more than 9 per 9. He's had a terrible season, lost the job as closer and even since returning from the DL hasn't been very good. He's thrown 19 innings, walked 16 and has an ERA over 4. He's due $9 million next year and based on the last season and a half it's hard to imagine any team wanting much at all to do with him. The Cubs could throw in a lot of money, but even then it's going to be difficult to get much of anything in return.
David DeJesus was signed a 2-year, $10 million contract in the offseason with a 3rd year team option. About the best that can be said of DeJesus's season is that he's produced .6 fWAR and .4 rWAR. He had a fantastic May, but other than that he's been pretty bad. His contract is more than manageable, but he's working on his second consecutive season of being a below average hitter. He is the kind of a guy a contender might like to acquire to be a 4th outfielder though. The Cubs will probably have to pay some of his contract and the Cubs won't get much in return.
There's Travis Wood who was off to a good start before falling apart. He's still relatively young and cost controlled so the Cubs probably won't be actively shopping him, but they'd definitely include him. Wood was part of the Sean Marshall trade so at best the team would be looking at a marginal prospect in return.
Alfonso Soriano is owed way too much to be appealing to teams and teams have appeared unwilling to even trade for him with the Cubs paying almost all of his remaining salary. That could change in the coming days, but I'm not betting on it. Even if they do trade him, it's just to free up a spot in the outfield. That's the best thing the Cubs will get in return because any prospect won't be worth much.
There's Reed Johnson, but he's a 4th or 5th outfielder so there's not much to acquire there. There are far too many C prospects and below to even speculate on what the Cubs could get, but it won't be impressive.
The Cubs entered the season hoping for rebounds from Ryan Dempster, Geovany Soto and Carlos Marmol because it would have helped increase the potential return on trades. They got a very nice rebound from Dempster, but his no-trade rights takes the leverage away from the Cubs when negotiating any trades. Soto and Marmol didn't rebound and even took a step back. Matt Garza was the other obvious trade candidate and he's injured. Look for a few minor trades, probably even one including Dempster, but don't expect much in return. The Cubs rebuilding process is on hold until the offseason.