Mark Twain once wrote, "There is no unhappiness like the misery of sighting land again after a cheerful, careless voyage." Larry Ellison, Paul Allen and Rupert Murdoch can empathize. They've parted with a large chunk of their earnings in order to stay happily adrift for days on end.

These men own some of the world's most technologically advanced ships, featuring helipads, cinemas, missile detection systems and music studios. Most of them are built to order. And all of these tricked-out floating palaces -- like Ellison's, which features a landing ship that can carry a SUV -- are priced out of this world.