Sea Change is good if slightly odd album. I can probably think of a hundred songs that relax me, so I'll just list some of my absolute faves:
Pet Sounds has a whole host of songs that I can chill to. If I had to pick one as the ultimate 'chill out' it would be Lets Go Away for a While.
Rufus Wainwright - loads of songs again. I'd pick 'Peach Trees' as a super relaxing, melancholic, beautiful song...
Feist: 'Now At Last'. Better than the original.
Devan Sproule - Stop By Anytime
Innocence Mission: plenty to choose from: Lakes of Canada or Lake Shore Drive would be my faves...
Wilco: 'Jesus, Etc'. Awesome awesome song.
Midlake: Van Occupanther. title track of their 2nd album, which is another one that is pretty melancholic all the way through. Takes a few listens to really appreciate it, but it is such a beautiful song..
The Shins: New Slang
Well, I could go on (I guess I listen to a lot of chilling, melancholic stuff...), so I just made a playlist instead: