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Here's a couple links to Epic Rap Battles of History, an indie channel started by a couple of comedians that has rocketed to #1 status on Youtube. Several of their videos have over fifty million views, and one even has over a hundred million (Romney vs. Obama, I think). There are plenty more than these two that are great, but most of these guys' videos have language that isn't site-appropriate. This pair is clean, though...and the first one has Weird Al in it ;-)
https://www.youtube.com/watch?v=8yis7GzlXNM
https://www.youtube.com/watch?v=6HZ5V9rT96M