Rappers like 50 Cent and T.I. have made a lot of noise about recording songs with the Susan Boyles and Lady Gagas of the world ("Susan Boyle is hot right now. I got to get her on a track, for real," says 50). Interesting pairings, to be sure. But a host of other hip-hoppers have recently decided to go another way, recruiting indie rockers for collaborations that have produced some great music, if not any major hits. (The Roots' indie-rock-sampling How I Got Over, out this week, includes ingenious collaborations with Joanna Newsom and Monsters of Folk. And there's Vampire Weekend fan Kid Cudi, Grizzly Bear–championing Jay-Z, and up-and-coming hip-hop group Chiddy Bang, whose entire career is built around rapping over indie rock.) Either way, there's a spirit of genre-bending collaboration in the air. Here's a look back at the past year or so of cutting-edge teamings-up, plus a few dream collaborations. Let us know what we left out.