A lot of us have our own musical preferences.
But what kind of music puts you in a relaxed mood? For me, it's not all classical music, but certain kinds. More often than not, when I turn the classical stations on, it's not the right kind of classical music; it's something that sounds too loud and excited, triumphant, or it's something that's too modern and complex. Most jazz is like this too.
Specifically this kind of music relaxes me:http://en.wikipedia.org/wiki/Classical_period_(music
From what I read, that's what "classical music" technically means, but we commonly misuse the term "classical music," to mean any type of symphonic or orchestral music over the last several centuries.
Some later stuff is great too, but that specific period of music best characterizes what I mean. Philip Glass, for instance, is "modern" but he claims to (and in my opinion) exemplifies the style from the classical period.
In addition to this...
"Chillout" and "Trip Hop", such as BonoboDJ FoodGroove Armada
Traditional Chinese and Japanese shakuhachi music is nice too
And 1950's love songs:
The best things in life aren't things.