He was playing for the Steelers, I believe, he was in the pocket and for some reason he decided to turn his back to the line of scrimmage - like he was going the wrong way, it was quite an odd decision - and he obviously had no idea that a defender was there to light him up. My immediate reaction when I saw it was, that's the hardest hit I've ever seen.
Sorry for not looking for any video on the youtubes.
Ryan Clark against Willis McGahee
http://www.youtube.com/watch?v=6d3R5aVR4K0
or
Ray Lewis vs the Browns
http://www.youtube.com/watch?v=n0oUPACk8K8&feature=related
Hines Ward lays out Ed Reed
http://www.youtube.com/watch?v=4QGKlluCU0o
Hines Ward against Keith Rivers http://www.youtube.com/watch?v=OPbraVljIrc&feature=related
not really the biggest hit ever, but it's Tebow
http://www.youtube.com/watch?v=9c3d9XcaIE8&feature=related
or perhaps some Shawn Crable owning Troy Smith would make your day better?
http://www.youtube.com/watch?v=lOmGMGUDPbk
Taylor Mays (link Below)
http://www.youtube.com/watch?v=DS1Bocgpw-M&feature=related
http://www.youtube.com/watch?v=XJKdpsZi_10
Benard Pollard ^^^
Shazor is hit number one
http://www.youtube.com/watch?v=dxVkjHWH1Rc
also, Alan Branch