"Shake Your Rump" (Beastie Boys)

"Shake Your Rump" from the classic album Paul's Boutique (1989) is the line between "the old Beasties" and "the new Beasties" for me.  All you have to do is listen to the first :30 of the track, and you instantly know that the frat boy shenanigans of 1987's Licensed to Ill are a thing of the past.  In fact, they'd had a highly publicized split with Russell Simmons, Rick Rubin, and Def Jam Records in 1988, the result of the band wanting a bigger cut of the profits and more creative control.  This ultimately led to the Beasties relocating from New York to L.A. and hooking up with the production team of John King and Mike Simpson (a.k.a. The Dust Brothers).  It also spawned weird rumors that the band was defunct because Michael "Mike D." Diamond had died from an overdose.  (I can't help but wonder if Rubin and Simmons might have had a hand in spreading those very rumors.)
Anyway, Mike D. wasn't dead, as he addresses in the second verse of the song (Well I'm Mike D., and I'm back from the dead / Chillin' at the beach down at Club Med...).  And the Beasties weren't kaput.  In fact, their tag-team flows were even more intricate and filled with pop culture references than ever before: they namecheck everyone from Fred Flintstone to The Brady Bunch's Sam the Butcher on "Shake Your Rump."  
On top of that, the song introduced the world to a whole new way of sampling recorded material.  No longer were the Beasties just copping some Black Sabbath riff and looping it over a single Led Zeppelin breakbeat; the track was one, big sound collage (there are at least one dozen identified samples on the track), culled from a vast library of vinyl and pieced together in completely unexpected ways.  It was as inventive as it was funky.
My favorite moment of this song is still that first instance when DJ Hurricane scratches in Afrika Bambaataa saying Shake your rump-ah! from his 1984 collaboration with James Brown, "Unity, Pt. 2," and then segues into that fantastic Moog synth growl from Rose Royce's "6 O'Clock DJ (Let's Rock)" from the Car Wash soundtrack.  It's still as fun and fresh as it was in 1989.