There are a lot of things to look forward to in 2012: Dr. Dre's Coachella appearance, the first photos of Jay-Z and Beyonce's baby, Blue Ivy, and the impending doom coinciding with this year's winter solstice. But before the world implodes into a fiery oblivion, several rap and R&B artists will make an attempt at what could be, according to the Mayans, their swan song. OK...