"Habanera" from G.Bizet's "Carmen" is a true masterpiece. Please, enjoy mezzo soprano Elina Garanca's performance and give my version a listen, too. 

Aria of Rosina from G.Rossini's "The Barber of Seville".
The original version is performed by fabulous soprano Edita Gruberova, while I suggest a new jazzy approach :)

Fabulous "Air on G String" from J.S.Bach's Suite No.3 is one of this compositions which, once heard, would be memorized and cherished deeply in ones heart. I love it so much that just couldn't resist to sing it!