Most of the older ambient music series by Brian Eno, a favorite among those would be Discreet Music. Nick Drake would do it for me to. I'm on board with Tobias for peacing out to Arvo Part's Alina, or Brahems Paws of the Black Cat - both are superb. In a very odd, hypnotic sense, try "Jesus Blood Never Failed Me Yet" by Gavin Bryars (with a little bit at the end by Tom Waits). Not for everyone though.
Most Peaceful Music you've Heard or Own
What music puts you in a deeply relaxed or peaceful mood -- something that could get you through a two hour traffic snarl feeling 'calm and collected'?