Perhaps my all-time favorite choreography is "Singin in the Rain" by Gene Kelly in the movie by the same name. The wistful delight of being in love gets captured in this lovely joy of the rain. The song, the dance, the facial expressions... one of the best moments in movie history.
Usher recreates the moment in his own suave way, and he earns a bounty of respect points!
I can just watch this clip over and over. Enjoy!