I know the internet is flooded with videos of people doing celebrity impressions, however, I think this video is pretty cool.  A couple of guys, Rob Cantor and Adam Horowitz write an original song and Cantor sings  it in 29 different celebrity voices.

I must admit, the woman impressions in this song are spot on, Cher, Billie Holiday, Christina Aguillera, etc.  I'm impressed.