Not everything on Wikipedia is original content. According to Webempires, the online encyclopedia cites and references over two million different websites. How else could they be considered accurate. There's an entire list you can check out if you have the time to spare and here's a list that highlights the top 50 sources.
Books.google.com, web.archive.org, and news.bbc.co.uk round out the top three, but there's also surprising references like MySpace and cricketarchive.com in the top 50 as well.