Guest List: Rihanna

One way to know you've made it in pop? A guest appearance by Rihanna. Adding the Bajan megastar's inimitable voice to any song—whether it's a synth-heavy soul ballad, an explosive hip-hop track, or a feisty ladies-only duet—gives it a dual jolt. Her A-list status platinum-plates it, while her tough-as-nails delivery of even the most bubbly choruses adds a streetwise edge.