I've run up a 19 minute piece by Sorabji. Called Ostinato it is the fifth movement of his Toccata Seconda a theme with 49 variations. It's made using sibelius and the Imperial Bosendorfer. You can listen to the mp3 here and if you would like to download the flac and read a bit more about it you can do so here where you can also access the first four movements if you get terribly interested.
Thanks for listening.