If you'd like to look back on 2009 with some poppy music, have I got a treat for you. DJ Earworm has created a mash-up of every single hit from Billboard's year end Top 25. You'll hear everything from Black Eyed Peas' "Boom Boom Pow" and "I Got a Feeling" to Beyonce's "Single Ladies," Taylor Swift's "You Belong With Me" and the Kings of Leon's "Use Somebody." Also featured are hits from Kanye West, Kelly Clarkson and, of course, Miss Lady Gaga. If you enjoyed this make sure to check out DJ Earworm's 2007 and 2008 mash-ups, too. Enjoy!