19. Rihanna feat. Ne-Yo - "Hate That I Love You"
"The best way to express an emotion like love is through storytelling," Ne-Yo said in a 2007 interview. "It makes it more, 'I can relate to this character in this song because I've been through something similar.'" He was talking about "Hate That I Love You," a beguilingly breezy track that he wrote for Rihanna's breakthrough album Good Girl Gone Bad. Ne-Yo and the Barbadian dynamo trade off lines about being crazy in love — in the bad way, alas — and the way their voices soar and blend is enough to make one hope that they eventually figure out a way to work things out, or at least duet again.