APA's Psychological Bulletin (and why wouldn't you be?), you'll find something especially relevant to your interests in the March issue. Psychologist Craig Anderson analyzed existing studies of 130,000 people from the U.S., Europe and Japan, and found that exposure to violent video games was associated with aggressive behavior and thought, along with typical accusations of an inability to foster positive social behavior. A rebuttal to the study from another psychologist and ESA chief Michael Gallagher is featured in The Washington Post article on the subject.
We're not doctors nor scientists ourselves, so we're not going to try to pick apart Anderson's findings. We, like Gallagher, are just going to point towards the research of two people who don't have such a huge axe to grind (as Anderson so clearly does). As Dr. Cheryl K. Olson and Dr. Lawrence Kutner wrote in their Grand Theft Childhood, "the strong link between video game violence and real world violence, and the conclusion that video games lead to social isolation and poor interpersonal skills, are drawn from bad or irrelevant research, muddleheaded thinking and unfounded, simplistic news reports."
Also, we'd ask that Anderson clarify if the tendency toward violent impulses was specifically sparked by playing Modern Warfare 2 online with a bunch of 12-year-old racist homophobes. Because, then dude, yes.