Will Lyman has to be the ultimate narrator.

[Locut0s]

http://www.imdb.com/name/nm0528164/

Here's a random Youtube clip of his narration voice for those who don't know him:

http://www.youtube.com/watch?v=5HXyJTXGTOk

I first got to love his narration work watching Frontline. Everything he does sounds epic lol.

I'd put David Attenborough a VERY close second.