Nandemonai or Weeeek by the Japanese Pop Group NewS. This is based on the days of the week in Japanese.
The main lyrics go like this:
Ashita kara, mata nichi getsu ka, hora,
sui moku, mawatte, kin do~
Nichi - Sun; Getsu - Moon; Ka - Fire; Sui - Water; Moku - Wood, Kin - Gold; Do - Saturn
~youbi and the words correspond to the days of the week starting with Sunday following the list above.
The catchy tune and wonderful dance moves have caused many videos with anime characters following the Nandemonai dance moves and many are beautifully done. Below is a video known as Fukkireta done (not by me) featuring the characters from the hit anime Deathnote!