For anime fans, JV (and a bit j-pop) and not know, So here's Nico Douga Nico Kumikyoku (Suite "Nico Nico Douga")

This is a series of video medley. The original video was created by Shimo (Servants) a sharing site Nico Nico Douga user. The number of views of those videos easily over a million. Moreover, these medley attracted people eager to affix voice over (the medley are speechless originally). So there are quite a number of times, some ranging up together 2000 voice (bringing together the various videos created).

Here are the original videos in order of appearance (finally… almost… because the original is on nico nico and requires Adobe to be registered to read) with some videos of occasions.

More detail Wikipedia (in English)

You can also get other medleys thanks to the Nico Nico Douga Medley Database. This site also contains a wiki containing varying information (tracklist, lyrics, …) on various medleys.