Have you noticed how rap stars have become like big name actors that give pop songs enhanced credibility? It’s as though pop songs are not good enough on their own without a rapper chiming in. It also might be because pop singers desperately need to prove their R&B credentials. Ironically, this trend also works in reverse. For example, would Eminem have gotten nearly as much mileage out of “Love The Way You Lie,” had Rihanna not also cooed along with that Detroit kingpin? These five examples of pop singers hanging out in the studio with rappers aren’t the first, and they certainly won’t be the last.