I wanted to add some sources to the terrific suggestions above. These are mostly links to web pages that talk about issues of objectivity in the mainstream press, but also some books that might help think through some of these issues.
-Unspun is written by the people who run factcheck.org, which is a really great resource for fact checking political information. You might monitor this site for information related to what happened in Boston, as well as wider discussions about security, immigration and "terrorism."
-Here's a very current critique of objectivity in the media.
-This blog post is structured as a Q and A, and it's intended to clarify how objectivity is used by the press as a concept that shields them from accusations of bias: http://pressthink.org/2010/11/the-view-from-nowhere-questions-and-answers/
This one gets at some of the underlying tensions related to bias and the blogger as the ideal "other" for journalists: http://pressthink.org/2011/03/the-psychology-of-bloggers-vs-journalists-my-talk-at-south-by-southwest/