The French Riviera has been attracting a jet-set clientele since, well, before jets were invented, but it hasn't lost its cache. In 2010, Russian billionaire Mikhail Prokhorov forfeited a $55M deposit after backing out of a $750M deal to buy the storied Villa Leopolda from banking widow Lily Safra.

On the French Riviera, but with tax benefits, Monaco has been drawing wealthy folks to its elegant lifestyle and lenient tax laws for generations. In 2010, British property developers sold off Edmond Safra's former penthouse for $305M. In other words, if you're looking for the world's most desirable real estate, just look for something the Safras owned.

London might get more sales volume, but the nearby countryside lands some of the largest deals. In August 2011, an unnamed Russian billionaire spent nearly $223M for Park Place, a 200-acre riverfront estate near Henley-on-Thames.

Those Russian billionaires who have chosen to stay in the country have flocked to Moscow and the surrounding suburbs, and brought their extreme tastes along for the ride. Evidence? This Zaha Hadid-designed mansion built for supermodel Naomi Campbell and her developer boyfriend Vladislav Doronin.

With the tech industry booming, it is no surprise that the suburbs of San Francisco that comprise Silicon Valley have seen their prices escalate recently, but the $117.5M sale of this nine-acre estate in Woodside to Japanese billionaire Masayoshi Son set a new regional record and, possibly, a U.S. record as well.

Wealthy snowbirds flock to Palm Beach each winter, but every year they seem to be getting richer and richer. If the rumors are true, the hotspot has seen one of its biggest deals ever go down recently, as Chicago-based hedge fund manager Ken Griffin is said to have spent a combined $130M on four contiguous oceanfront properties.

The Indian financial hub is home to more than 20 billionaires, but only one billion-dollar house. Antilla, as the towering single-family residence is known, was built by businessman Mukesh Ambani on land purchased for just $4M, a pittance next to the alleged cost of construction.

Paris is the world's most expensive property market, on a per-square-foot basis, and even before income taxes skyrocketed to 75%, rich Parisians were keen to cash in. In 2010, this historic mansion on Avenue Foch was listed for $140M.