For the last few years, DJ Earworm has mashed up the biggest songs of the year.  And here they are:

Billboard has some of the backstory, including why DJ Earworm didn't use a couple of the biggest earworms of 2012, (Call Me Maybe, Gangnam Style), along with links to previous United State of Pop mashups.

(Personally, I think it's a better work without the video.  And DJ Earworm kindly allows for free downloads of the audio track at his homepage.)

Meanwhile, BuzzFeed reports on the most popular YouTube videos of 2012, both musical, and non-musical.