Kumikyoku Nico Nico Douga (組曲『ニコニコ動画』) is what video medleys featured on the popular Japanese video sharing site, Nico Nico Douga, are called. It is also the title of the most popular video in the official series. They usually mostly compose of songs made famous on the site.
The last official video was titled Nanairo no Nico Nico Douga (七色のニコニコ動画) and was uploaded on June 3, 2009.
((sourced from Know Your Meme entry))