This past Sunday at the Made in America festival, Pearl Jam brought Jay-Z (also the show's organizer) onstage to perform a live rendition of "99 Problems." This garnered mixed reactions - the crowd seemed to dig it, but not everyone thought this was a great idea. Rap should stay on one side, rock on the other. I beg to differ, but hey - not everyone likes their peas to touch their mashed potatoes, either. 

Musical history has definitely seen some odd pairings. Some have worked (Run DMC and Aerosmith, "Walk This Way") and others have not. Here are a few notable collaborations, from decent to downright awful...

1. Half Canadian, half just...wow. Celine Dion teamed up with R. Kelly in 1998 for "I'm Your Angel," a sweet 90s-pop track but in retrospect, more creepy than inspirational. 

2. Ozzy Osbourne and Miss Piggy, "Born To Be Wild." Amazing and wonderful and weird in the best possible way! This is one of the things that makes me proud to have been a Muppets-loving kid. Piggy would go on to perform duets with the Jonas Brothers and the Cheetah Girls, but I stand firm that this duet with Ozzy was one of her finer moments by far. 

3. The Pearl Jam jam wasn't Hova's first foray into rock collabs. 2004 gave us Linkin Park and Jay-Z's Collision Course: big pimpin', nu metal-style. 

4. Insane Clown Posse invited Tila Tequila to join them onstage during the 11th annual Gathering of the Juggalos in 2010. Like most nights involving tequila, this did not end well. 

5. Paul McCartney and Stevie Wonder, "Ebony and Ivory." This duet has taken some flack, but the fact that these two legends are onstage together (and in this vid, years later!) outrules any possible negative critique. It's Paul McCartney and Stevie Wonder, dammit! 

6. Bob Dylan and Johnny Cash. Again, no complaints here - except that I was not in the audience! 

This list is by no means exhaustive - feel free to add to it in the comments! 

b