Captain Paul Allen, founder of Microsoft with Bill Gates.
Mates Allen holds a massive annual party for some of the world's biggest media executives onboard, with one particularly envy-stricken guest being Time Warner's head, Dick Parsons.
Drops anchor This summer, your best bet of seeing her is off Spain's east coast.
Helipad? Who needs a helipad when you've got a personal submarine? Octopus is, at 414ft, the largest yacht in the world, and it has features to match, including a 59ft landing craft.
Captain Prince Khaled, Saudi Arabia's deputy defence minister. He's keen to sell, though, for £39m.
Mates Legions of eminent oceanographers. The prince takes a philanthropic interest in maintaining threatened coral reefs, and he's loaned out his yachts to scientists for years.
Drops anchor Famously moored in Nice this summer, right next to Stelios Haji-Ioannou's EasyCruise aberration.
Helipad? The most extraordinary feature on this 265-footer is the coral-reef aquarium visible beneath the main pool.
Captain Nasser al-Rashid, Saudi Arabian gazillionaire.
Mates King Fahd and the Saudi royal family. Al-Rashid is also a big contributor to George W Bush, but it is unknown whether Dubya's drawl has been heard on board.
Drops anchor Monaco, or any other Mediterranean destination where you can buy a beer for €100.
Helipad? Why, of course. Not only does Lady Moura have its own $25m helicopter, it also has four other boats stored on its fifth deck. When the rain comes in, you can head to the 59ft dining table where staff will wait on you.
Captain Once owned by J Paul Getty, the Talitha G is now available for charter for £200,000 a week.
Mates Tom Cruise and Nicole Kidman found their sea legs together. In 1997, the British royal family observed Cowes Week from Talitha G's polished decks when Britannia was out of commission.
Drops anchor Currently bobbing off Portovenere, on Italy's Ligurian coast.
Helipad? There are six staterooms aboard this beautifully restored yacht, as well as a vast main-deck dining room. The boat is kitted out with Art Deco fittings, which were designed by Jon Bannenberg and son Dickie.
Captain René Herzog, the former racing car driver, and his wife, Brigitte.
Mates Available to anyone willing to part with some serious money (the yacht's asking price is £38m), but often the only company René and Brigitte have is their dog, also called Giant.
Drops Anchor From the Arctic to the Caribbean, there is nowhere Giant won't travel. But in the summer, look out for her red hull in the Aegean.
Helipad? No, but this converted ice-breaker does have a garage specially made for a Dodge Durango and a Bentley. The Master Suite is designed to resemble the Hermitage, while others have been given the "real fake" treatment in the style of Claude Monet and Salvador Dali.
Captain Greek shipping tycoon John Paul Papanicolaou now owns what was once Aristotle Onassis's flagship. But only modern Onassises can afford to charter it at the gargantuan rate of $1.54m (£900,000) for two weeks.
Mates Christina O is frequented by celebrities and statesmen alike. South African President Thabo Mbeki was the last big name to walk its varnished planks, while Richard Burton and Elizabeth Taylor were guests of Onassis.
Drops anchor Anywhere in the Aegean.
Helipad? Christina O is a billionaire's wet dream. Lavish features such as the 1,500sq ft sunbathing area and the upper-deck bar dedicated to champagne mix easily with details such as the lapis lazuli fireplace in the room once enjoyed by Burton and Taylor.
Captain The Greek tycoon Yannis Latsis, who died last year, used to own the boat. Now, his family charter it to select guests for $100,000 a day.
Mates Prince Charles and Camilla Parker Bowles were frequently treated like royalty on the Alexander.
Drops anchor All around the Med, but largely off Athens.
Helipad? Not quite, but "Alexander the Great", as she's also known, boasts a pool, Jacuzzi, nightclub, cinema, music room, and guest rooms to sleep 60.
Captain Liveras Yachts of Greece is arranging a part share of Annaliesse - the yacht is also the most expensive in the Med to charter at $840,000 (£480,000) a week.
Mates The new Russian oligarchy and Eastern seaboard billionaires.
Drops Anchor Ile Ste-Marguerite, near Cannes.
Helipad? No, but you could easily land a helicopter on the private deck of the 360sq ft Owner's Suite. There are also Michelin-starred chefs, Roman baths, cinemas, a library and an onboard hospital.
Captain Once owned by the American publisher Walter Annenberg, Princess Tanya is now in the hands of the yacht magnate Andreas Liveras.
Mates This is very much a boat for the discreet billionaire rather than hordes of A-listers.
Drops anchor All over the Med, most often in Sardinia.
Helipad? No; understated opulence is the order of the day. Three Swarovski crystal chandeliers hang over her dining table, while the saloon and dining room are separated by double-sided silk curtains. There's no need for a stereo; the ship has its own violinist and pianist, who do requests.
Captain Paul Allen, again.
Mates Cameron Diaz and Jack Black have partied on board.
Drops anchor Tatoosh often shakes its tush at Cannes.
Helipad? How else are the celebrities going to get there? Tatoosh is also the launchpad for a variety of millionaire's pursuits, including sailing, where the maritime plaything she keeps lashed to her upper decks comes in useful.
Captain The Turkish flash-Harry shipping magnate Kahraman Sadikoglu runs the vessel, but you can don the skipper's hat yourself for $280,000 a week.
Mates Claudia Schiffer, Robert De Niro, Hugh Grant and Sylvester Stallone have trodden the boards of the Savarona.
Drops anchor Off the harbour at Cannes.
Helipad? Certainly not. Savarona, built in 1931, is a paragon of old-European excess. She has a crew of 55, a Turkish bath built from 260 tons of marble, and 17 suites more than 400sq ft in area. There is also a secret passage connecting a private stateroom to the crew's stateroom.
Captain Atlantis II was built as part of an ongoing game of one-upmanship between its owners, the Niarchos family, and Aristotle Onassis.
Mates Monaco playboys and Formula One drivers.
Drops anchor Atlantis II is a full-time resident of Monaco harbour. If this monster has to pop out for groceries, she must reverse due to her size.
Helipad? When the ship first plunged into the deep in 1981, it was equipped with a retractable swimming pool on the deck (because Aristotle had one on Christina O).
Captain Roman Abramovich, owner of Chelsea FC.
Mates The Chelsea team are always asking for holidays on one of their boss's four yachts, but it is unclear whether he has caved into this contract demand.
Drops anchor Malta.
Helipad? Naturally. But compared to Abramovich's other yachts - one of which, Le Grand Bleu, was called "big and ugly and new-fangled" by Shirley Bassey - Pelorus is elegant. She's curvy, with outsized windows and an understated colour scheme. Her crew of 40 reportedly cleaned several shops in Malta out of luxury food to satisfy guests.