Wikipedia is the number one free source to get any kind of information. It provides a wealth of information with more than 26 billion pages of content. Though the quality and accuracy of Wikipedia data has always been questioned, but the editors of Wikipedia, known as Wikipedians, are vigilant with ensuring that the data in Wikipedia is current & accurate. Various Studies have also shown that Wikipedia Data is almost as accurate as the Encyclopedia Britannica.
Check out this Infographic from Open.org which highlights how Wikipedia has revolutionized research over the years and how it has now become a reliable fountain of information and knowledge.