"Who is the Master?" Frank Caliendo
Of impressions, that is. I used to think Kevin Pollak was the best, and I still like his Captain Kirk and Christopher Walken, but Frank Caliendo (below) has got to be the best of all time. This collage is a bit too quick in the beginning, but just give it a few minutes, it gets really good. Also, this excerpt is probably at least a few years old; he's gotten better since then, especially his George Bush.