Tchaikovsky - Symphony no. 5 in E minor
Tchaikovsky composed his fifth symphony to prove to others, and to himself, that he wasn't "played out" as a composer. He needn't have worried. It's a fantastic symphony, containing gorgeous melodies and deeply felt emotion - traits that are typical of Tchaikovsky. Rather than the work of someone in decline, it's the work of a composer who was very much at the peak of his powers.