Depends on how you define beautiful, but I've got a hankering for Miaskovsky's 5th Symphony.
I would also count Myaskovsky's elegiac and haunting Symphony no. 27, as well as his beautiful Cello Concerto, among the most beautiful works of the last century. Written in the final years of his life (the concerto in 1944 and the symphony in 1949) these two works poignantly represent the "final breaths" of the romantic tradition which Myaskovsky so dearly loved.
I concur!
I would add also:
Bax's Third Symphony
Atterberg's Sinfonia per Archi
Eller's Five Pieces for Strings
Tubin's 4th Symphony
Silvestrov's 5th Symphony (as if nature is unfolding onto something otherworldly).
Lydia Auster's Piano Concerto