The private island is perhaps the ultimate toy of the absurdly wealthy. In today's tough real estate market, some kind of private island is probably available to anybody with an extra seven figures rattling around in their wallet, but you still probably need eight to get into the luxury market. Naturally, the sky is the limit if you want genuinely princely amenities - jet port, deep water harbor for your yacht, a few villages worth of servile native house elves.
Personally, I want more. If I make it big I plan to buy Madagascar or New Zealand.