Main Page - Wikipedia

Now this has to be the most informative site on the web. I suppose it all depends on what you are looking for but... I used this site extensively for my political economy class at grad school. I never went without an answer.
The idea behind it is that it's an open source encyclopedia that anyone can contribute to. Have some great specialized knowledge just waiting to burst out of your head? Well, write it down here and let the world know all about it.
One caveat with this though. Anyone can write anything they want so you don't always get an unbiased opinion. Check out the posting for capitalism. Obviously some left-wing Marxist dog was allowed to express his or her opinion.