June 12 [14:00 EDT] -- When a number of musicians turn up in the same place, you can expect some creative cross-pollination, and that was certainly the case at last weekend's Tibetan Freedom Concert.

Fans who turned up at New York's Randall's Island hoping for a few surprises got their fair share through these unique collaborations. Few could have expected Blues Traveler frontman John Popper to walk in from the wings and lend his harmonica skills to Taj Mahal's take on the nugget [article id="1440317"]"She's Complicated" [Live 1MB QuickTime][/article]. While the Taj Mahal set had worked Sunday's sun-baked crowd into a mellow, bluesy groove, the appearance of Popper snapped most to attention and got them in a dancing, swaying mood.

Likewise, R.E.M.'s Michael Stipe and Mike Mills (with help from Patty Smith's bass player Tom Shanahan) slipped the crowd a Mickey with a delicate set that included low key numbers like "Electrolyte," "Undertow," and "New Test Leper."

Then, after Stipe beckoned "Eddie, could you come out here please," the trio was joined by Pearl Jam's Eddie Vedder and Mike McCready (both wielding guitars) for a take on Iggy Pop's [article id="1440319"]"The Passenger" [Live 1MB QuickTime][/article]. While the group's performance had a somber sound, the mere presence of this R.E.M./Pearl Jam monster was enough to re-energize the crowd.

One group that had no shortage of energy last weekend, Rancid, even brought some friends out to give their set an extra charge. While the band was flooring the masses with its revisionist punk on snarling melodic tracks like [article id="1440321"]"Ruby Soho" [Live 1MB QuickTime][/article]and "Timebomb," it reached into its bag of tricks and pulled out the horn section from the ska outfit the Stubborn All-Stars for "I Wanna Riot." Even though the band's set didnít seem to need any help, the horns kicked the intensity level up a notch or two as hats, shoes, and blankets began flying

up from the bouncing masses gathered at the front of the stage.

Fans may have been just as surprised by one collaboration that did NOT happen: despite countless screams from the audience, the Beastie Boys did not join Biz Markie during his performance Saturday evening.