One word: Muzak!
This may dismay you. On the other hand there is some good quality muzak out there (he he

)
Satie - Gymnopedies and Gnossienes.
Debussy – La fille aus cheveux de lin, Arabesque no. 1, Clair de lune, Reverie
Chopin – Nocturnes & Waltzes, Fantasie Impromptu
Mendelssohn – Songs without words no. 1, no. 18 & no. 25.
Field Nocturnes
Myers – Cavatina
Grieg – Arietta
Schumann – Reverie, Strange lands, Drei Stucklein (op. 99 no. 1), Schlummerlied (op. 124 no. 16)
Liszt – Consolations, Liebestraum
Bach prelude 1 of the WTC1
Beethoven 1st movement of moonlight, 2nd movement of Pathetique, Fur Elise
Schubert Impromptus Op, 90 no. 3 and op, 142 no. 2 (without the f and ffs).
MacDowell – To a wild rose
Standards like “As time goes by”, Cole Porter, etc.
You can also try Ludovico Einaudi. His music is a big hit at the UK at the moment. It is just ideal for this sort of environment.
You get the idea.
All of those of course played softly and without too much dynamics, In short: Background music.