Original from rabiesx86/PonyDub: http://www.youtube.com/watch?v=GyXg_MJeeuw
Even more original from Renard: http://www.youtube.com/watch?v=BI6veK6ARGU

All sounds with pitches are from the show except the Electronic Bass synth. All sounds have pitch? Whatever.
Sources:

Fluttershy "What": Season 1 Episode 23
Fluttershy "Hush": Season 1 Episode 17
Pinkie Pie "Hay": Season 1 Episode 21
Twilight Sparkle "Fly": Season 1 Episode16
SweetieBelle "Jelly": Season 2 Episode 17
AppleBloom "I": Season 2 Episode 17

I saw the original a while back and I loved it, but I wished they had remade the song from scratch in it. So that's what I did.

as for me, You can find some of my stuff here:
Soundcloud
http://soundcloud.com/the-phony-brony

Facebook Page:
http://www.facebook.com/pages/PhonyBrony/224355487656606
Twitter:
@phonybrony
Download this song:
http://dl.dropbox.com/u/64168695/IntensivePonyUnitPhonybrony.mp3
Download this remake with the instruments and not the ponies:
http://dl.dropbox.com/u/64168695/intensiveCareUnit.mp3