I've been looking for a quick way to uncover biases in the news I take in.  I found an interesting study that attempts to quantify media bias by source.  Notably, it was created by two conservative professors (who have been criticized for their method of scoring), but it looks like an interesting piece to consider and could perhaps be used as a point of reference.

http://www.sscnet.ucla.edu/polisci/faculty/groseclose/Media.Bias.8.htm