Beautifful (to me) means rich, melodic, layered themes. I know everyone has their own definitions but for me I tend to think more along classical music lines as beautiful.
RAGTIME for sure. A great deal of the score for GREY GARDENS. Much of LIGHT IN THE PIAZZA (when it isn't getting too self-conciously angular), The choral segments of TITANIC and most of PASSION. I would rank all of tehse not only as great theatre writing but musically great concert music. I would love to hear the Boston Pops play a suite from any of these. (There is a suite from RAGTIME as a bonus track on the OBCR.)
Secondary to this, not the entire score but there are beautiful melodies to be found in GRAND HOTEL, ASPECTS OF LOVE, BEAUTY AND THE BEAST, STEEL PIER, and SCARLET PIMPERNEL (Storybook!)
Sad that of the shows playing now on Broadway with new/original scores I can't name one that I feel contains a wealth of beautiful music.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com