I love this kind of stuff: a "flash mob" sings the Hallelujah Chorus from Handel's Messiah in a shopping mall food court. Even better -- some bystanders (bysitters?) join in! And the sound quality is excellent given the circumstances. Thank you America... this probably never would be organized in Germany. Wish I could have been there.
Letting the-nerd-within loose again: a more, um, clinical version can be found in the HP 3314A Function Generator and Frequency Synthesizer. It seems that one of the equipment's internal test functions, coded by the developing engineers, plays the Hallelujah Chorus (unfortunately monophonically, but I'll bet very accurately). What is the 3314A? You don't know??? I thought everyone uses a variable symmetry, phase-locking, low-distortion waveform generator!
And to wrap things up, two of the all time great "performance art" videos (not Christmas-related):
Hammer Time Mob Dance
and Frozen Grand Central Station (from ImprovEverywhere, check out more vids on their website)