Classical is good, not necessarily orchestral. Since I play the piano, I prefer to listen to piano music, and it's as relaxing as anything.

Some of the BEST relaxing yet beautiful piano pieces:
Brahms - Intermezzo in A, op.118, no.2
Liszt - Consolation #3, Un Sospiro
Mendelssohn - "Songs without Words". (Listen to a few of them, they're all good. Some just aren't "relaxing" )
Debussy - Claire de Lune, Reverie, Arabesque #1

And, just about any version of the Canon in D is good!

I think I have plenty more, but I'll leave it at that for now.