good atmospheric rock/metal

I second/third/fourth/ whatever

Agalloch
Ulver
The Mars Volta
Godspeed You! Black Emperor
King Crimson
Deftones (White Pony only)

and add

Radiohead
Burzum
Emperor
A Silver Mount Zion
Pink Floyd
Shape of Despair
Robert Fripp (you can't get more atmospheric then his soundscapes...)

Theres plenty more, downloading Pelican right now