There is a huge amount of comforting music from all periods and from many
places.  To generalize, moderate dynamics, relatively simple harmonies
(whether in major, minor or modal modes) gentle melodic lines, and
elemental forms of song and dance are generally comforting, I think,
although unlike some who have responded, I often find Viennese waltzes
irritating rather than soothing.  Not sure why--but probably there is
just more harmonic resolution than I can stand.

Personally I could describe as "comforting" most Baroque music and
quite a number of classical, romantic and modern concertos, notably
Mozart's for flute and harp, Beethoven's 4th, 3rd and 1st piano concertos,
Shostakovich's 2nd Piano Concerto, the violin concertos of Beethoven and
Mendelssohn, and others.  Other random pieces: Debussy's Rhapsody for
Saxophone and Orchestra,  Dvorak's Slavonic Dances, Kodaly's Peacock
Variations, Elgar's Enigma Variations.  Symphonic music, which thrives on
tensions, in general I do NOT find comforting, with some exceptions, such
as Beethoven's Pastoral and 4th, Dvorak's 8th, Prokofief's 7th, Thomson's
Symphony on a Hymn Tune, for instance.

I was very struck by Aaron Rabushka's nomination of Tchaikovsky's 5th and
some time I plan to write about the long and complicated history of my
feelings about that piece.  (I was also struck by Aaron's dismissal of
Brahms' First, which has so many things in common with the Tchaikovsky,
though it is of course very different.)

Jim Tobin