I've got to say that my favorite impressionist ever is Stevie Riks. If you've never heard of him or seen his brilliant work, go on his Youtube page and check him out. Here's my favorite:
Here's the link to the page if the embedding doesn't fit your screen.
He has plenty more where that came from (if Youtube hasn't shut him down yet again for "copyright infringement." It hasn't seemed to occur to them that he's just a really damn good impressionist!) so you should check out his stuff and support him.
If it helps, he does killer impressions of The Beatles and David Bowie