I am a huge fan of the Wikipedia.
Wikipedia is a Web-based, multi-language, free-content encyclopedia written collaboratively by volunteers and sponsored by the non-profit Wikimedia Foundation. It has editions in about 200 different languages (about 100 of which are active) and contains entries both on traditional encyclopedic topics and on almanac, gazetteer, and current events topics. Its purpose is to create and distribute a free international encyclopedia in as many languages as possible. Wikipedia is one of the most popular reference sites on the internet, receiving around 60 million hits per day.
Now that you have the background you can understand why this is hillarious…
Billed as the content-free encyclopedia that anyone can edit.
My two favorites so far: