Chopin's Nocturnes are certainly among the most beautiful piano pieces I've ever heard; extremetely elegant, refined music which at the same time is so passionate and intense, with a poetical touch of melancholy. My favourite set is the Ashkenazy; after that, the Rubinstein, the Barenboim and the Pollini. Besides showing a wonderful technique and an excellent virtuosity, Ashkenazy really seems to be able to capture the deep mood of these works, the atmosphere he creates is absolutely thrilling.