First and foremost, the legendary Radiohead.
Thom Yorke is backed by the USC Trojan Marching Band (who, in my opinion, stole the show. They rocked!)
Hopefully the video is still up (copyright, you know...don't the powers that be realize these videos sell their records? Hello...). See it here.
Also, Adele, with Jennifer Nettles from Sugarland, singing "Chasing Pavements" (the first two YouTube versions I originally saved have already been pulled. So frustrating)