The American Express Centurion card is so elite that the cardholders themselves are the only ones who know about its benefits. It's invitation-only and AmEx declined to offer information about the card's perks or requirements. "We like to keep it private for that particular group," a spokeswoman said.

One thing is for certain -- it's extremely pricey: an online cardmember agreement states that the initiation fee is $7,500 and annual membership costs $2,500.