These make me laugh, in a good way. I'm attaching the links to the original song from the Beyonce one because I think they did a good job sticking close to the rythym of the lyrics and all.
Also, this guy does a great impression voice-wise.
http://www.youtube.com/watch?v=nrnNC5toyeo - Original. Embedding has been disabled but if you follow the link you can get to it.