3B Chris Johnson was traded to the Diamondbacks for OF Marc Krauss and IF Bobby Borchering. (Borchering has actually been playing OF this season, but the Astros have listed him as an IF in the release so they may be planning on moving him back to the 3B/1B which he played earlier in his career.)
Bobby Borchering is currently listed as #11 on Jonathan Mayo's list of Arizona's top 20 Prospects. He is a switch-hitting slugger with plus power and a high strikeout rate. Baseball America had him ranked at #10 in the Diamondbacks system coming into 2012 noting he has "as much raw power as anyone in the system." He was recently promoted from Hi-A to AA.
Marc Krauss is currently listed as #20 on Mayo's list of prospects for Arizona. Baseball America had him at #16 coming in to the 2012 season. The lefty hitter started out strongly in his pro career but had a significant drop-off in 2011 causing him to repeat the AA level where he is having some success this season, including being named a Southern League All-Star. According to both sources, his bat remains a question mark.