Franck - Prelude, Aria et Final - the neglected sibling to the famous Prelude, Chorale et Fugue.
The problem is that the Prelude, Aria et Final are very hard to play well from a musical standpoint. A lot of recordings are quite heavy and boring, but I find this music has a lot of life and interesting and beautiful things going on if you play it well. I particularly love playing the Aria, it envelops you in such a blissful peace, while still having something occasionally bittersweet about it.