The main piece aquired in the Ryan Dempster trade was 21 year old Christian Villanueva. Villanueva was signed as an international free agent out of Mexico by the Rangers in 2008 and just recently turned 21. He's played the entire season in High A.
His first season in the US was in 2010 in the AZL. Over 210 plate appearances he hit .314/.365/.431. That was good for a .370 wOBA and 127 wRC+. He didn't show much power and hit just 2 home runs. His ISO was .117. He's only 5'11, 160 so he's not going to hit for a lot of power, but he has started to hit for some power.
Promoted to A ball in 2011 he continued to hit the ball well. Over 529 PA he hit .278/.338/.465. His wOBA was .365 and wRC+ was 122. He hit 17 home runs and posted a .186 ISO.
Following the increased power, Baseball America ranked him 9th in the Rangers organization and 100th among all prospects. Their scouting report entered the season said this:
Scouting Report: Villanueva has a short, compact swing with a balanced load and good bat control. He has an advanced approach at the plate, though he can get pull-happy at times. There are mixed opinions on his power, as he presently has line-drive sock but some scouts see at least average potential. He doesn't project as a basestealer, but he has sneaky quickness and instincts that allowed him to swipe 32 bases last year. Villanueva is equally as impressive at third base as Mike Olt. A plus defender, Villanueva has soft hands and easy actions. Despite average speed, he has a solid range thanks to his first-step quickness and instincts. He has above-average arm with good carry and accuracy.
The Future: Scouts compare Villanueva with countryman Vinny Castilla. With Adrian Beltre in Texas and Olt ahead of him in the system, Villanueva spent time during instructional league at second base, where there would be reduced pressure on his bat. He'll play in high Class A in 2012.
With the exception of his defense, he doesn't stand out in any one area. He's a solid hitter and has some power and some speed. He definitely has the glove to make up for whatever offensive deficiencies he may have. His walk rate is one area to watch. It's down below 6% this year after being a mediocre 7% last year. However, he does make up for what might be a lack of patience by getting hit by a shitload of pitches. He was hit 12 times last season and he's already been hit 20 times this year. It's led to his OBP being a 70 points higher than average, which is good.
After the trade, BA wrote this about Villanueva:
The Rangers are loaded at third base with Adrian Beltre in the majors and stud prospect Mike Olt in the minors, which made the well-regarded Villanueva expendable. Signed out of Mexico, he ranked No. 100 on our Top 100 Prospects list entering the season. Villanueva has a broad base of tools that include a solid bat, potential average power, fringe to average speed with good instincts on the bases and standout defense with soft hands and a strong arm at third base. He's just 21 and in high Class A, so he still needs time to develop. He'll have to tighten his strike zone, and some scouts question if he'll grow into enough power to be a big league regular at third base.
Josh Vitters is really the only Cubs 3B prospect that's anywhere close to being ready so this is a nice addition. As far as I know, there's been no word on where any of the prospects the Cubs acquired will be sent, but I haven't spent a great deal of time looking around for that either.
You can check out this nice article about Villanueva over at Fangraphs too.