This singer pretty much nails it in his impression of 29 different celebrities in one song.

Rob Cantor (accompanied by Andrew Horowitz) performs an original song, "Perfect," in the voices of nearly three dozen celebs, including Frank Sinatra, Adam Sandler, Shakira, Chrisopher Walken, Christina Aguilera, Randy Newman, Smeagol/Gollum and a whole lot more. I think the best ones are Gwen Stefani, Billie Holiday and Britney Spears, but wait until you get to the trumpet! (Seriously, don't miss the trumpet!)

Some folks here (shall go nameless to protect their anonymity) have questioned if all of the voices are done live or if he used playback for a few of them and lip-synced
along. So maybe fake? I don't know. All the Debbie Downers will point out how it sucks/isn't real/is stupid. Whatever the case may be, this guy has some pretty amazing skills.