You don't always have to understand the words ...
Puccini - 'Recondita armonia' (Tosca)
Donizetti - 'Una Furtiva Lagrima' (L'elisir d'amore)
Verdi - 'O Terra, Addio' (Aida)
And for when you do ...
Elvis Presley - 'Kentucky Rain'
Jayhawks - 'Blue'
Jeffrey Gaines - 'Hero'