Beyond the Boxscore has posted densive rankings for each position based on runs above average derived from zone rating. You can read about the methodology if you are more interested. Interesting observations:
Adam Everett is a bad ass shorstop.
Lance Berkman is a serious asset at first base (while likely a liability in the outfield).
The Rangers infield is right at average, a significant improvement over last season (with the exception of Teixeira, who has fallen off). All Ranger infielders contributed or cost less than one run with their defense this year, with the exception of MY who has contributed 1.5 runs. This conforms with my perception that his defense at shorstop has improved this year.
The outfield is very poor defensively, with GMJ, Wilkerson, and Mench all among the worst defenders at their position. Mark Derosa is the only Ranger outfield who has not cost the team runs, contributing 2.2 runs to the team through his play in right field.
You can view the rankings here: