From the Bethesda Blog:
"Two weeks ago, Pete discussed that that we've been working hard to bring Shivering Isles to the PS3 either by way of PSN or a standalone disc. Well today we've got some good news. To make the game accessible to everyone, we've officially announced that we're releasing the game as a standalone disc. Just as with the Xbox 360 version, you'll still be required to already have a full version of Oblivion to play Shivering Isles.
Shivering Isles is scheduled to ship in the North America on November 20th for $29.99."