There are thousands of very beautiful pieces of classical music. Here you can listen some of my favorites among the most famous ones. All these files can be obtained from open sources (Youtube, Wikipedia, etc.).
F. Cilea. Opera: L'Arlesiana. Federico's aria "Lamento di Federico" (translation). Performance: Alfredo Kraus.
G. Verdi. Opera: La Traviata. Violetta's aria "Addio del Passato" (translation). Performance: Anna Netrebko.
P. Solozábal. Zarzuela: La Tabernera del Puerto. Leandro's Romanza "No puede ser" (translation). Performance: Plácido Domingo.
F. Moreno Torroba. Zarzuela: Luisa Fernanda. Luisa Fernanda and Javier's duet "Cállate Corazón" (translation). Performance: Nancy Herrera and José Bros.
J. S. Bach. Cantata BMW 140, 4th movement "Zion hört die Wächter singen" (translation). Conductor: Wolfgang Gönnenwein.
K. Jenkins. The Armed Man: A Mass for Peace. Benedictus (translation). Conductor: Karl Jenkins.
A. Dvořák. Symphony No. 9 (From the New World), 2nd movement. Conductor: Rafael Kubelik.
J. Rodrigo. Concert Fantasía para un Gentilhombre, 1st movement. Performance: Narciso Yepes.
E. Morricone. The Mission Soundtrack. "Gabriel's Oboe". Conductor: Ennio Morricone.
F. Liszt. Hungarian Rhapsody No. 2. Performance: Valentina Lisitsa. See also the famous Tom and Jerry's cartoon here.