There are a lot of comments in this thread talking about a strong bias in Wikipedia, but I don't see any examples. I have no doubt that there are some articles that are biased, particularly in less popular areas that get less attention, but overall, Wikipedia does a great job maintaining a neutral point of view in its articles.
I do get the impression that what people perceive as bias is often simply neutrality. If you think yourself the victim of an evil cabal of your political opponents, then a neutral description of the facts might seem like an attack.