do you already know of electronica artists you like? What is your definition of ambient?
My INTJ roommate likes Gabriel & Dresden:
MySpace.com - Gabriel & Dresden - SAN FRANCISCO, US - Electronica / Pop / Progrsv House - www.myspace.com/gabrielanddresden
He also likes deadmau5 (listen to Faxing Berlin):
MySpace.com - deadmau5 - Toronto, CA - Other / Electronica - www.myspace.com/deadmau5
Hernan Cattaneo seems sort of ambient:
MySpace.com - Hernan Cattaneo - Buenos Aires - House - www.myspace.com/hernancattaneo
For the above two DJ's, I'd recommend downloading their sets (probably not available on iTunes) rather then their individual tracks.
I would consider the older Aphex Twin or Authechre (Amber) albums ambient.
I like the modern classical composer Ernest Bloch (and others but can't remember offhand).