Now my all time favourite impression has to be Kevin Pollack doing Christopher Walken:
http://www.youtube.com/watch?v=PcKQGiih8_A
http://www.youtube.com/watch?v=WSEfUkAm8-0
But a close second has to this fellow’s impression of Tom Cruise from the film “Superheros”. The gesticulations and mannerism are dead on: