The world's most worthless currencies :

Zimbabwe

As Americans worry about the rate of inflation exceeding 4 percent, we should consider Zimbabwe, where the inflation rate broke the shocking 100,000 percent mark and the country released a 10 million-dollar note. One US dollar now buys 30,000 Zimbabwe dollars on the official market, having previously earned 250 Zimbabwe dollars. However dealers said that on the illegal market, $1 was buying 250,000 of the Zimbabwean currency. A roll of toilet paper in Zimbabwe costs $145,750, which is about 69 American cents. Currently the smallest banknote in circulation is the $500 bill.

Vietnam

Vietnam became the latest Southeast Asian country to devalue its currency, as Asia's financial turmoil showed signs of pummeling even the most protected regional markets. The Vietnamese central bank allowed the country's currency, the dong, to slip to a new controlled rate of 11,800 to the dollar, a 5 percent devaluation. The bank allows the dong to trade within a 10 percent band around the target rate, and the currency fell to its floor of 12,980, an all-time low. The value of the biggest banknote in the country (500,000) is $31.37. Starting with the early 1980 the embargo of the United States stopped the exports from Vietnam, which lead to price controls and an abundance of dongs printed in the country.
Like China, Vietnam does not allow its currency to be traded freely on currency markets, so any devaluation is essentially a political decision. But markets played a role. Traders say that currency swap market transactions, which had been running at $8 million a day at their most active, have been less than half a million dollars a day recently. Many companies have hoarded dollars or arranged trades on the black market rather than exchange dollars for dong at the official rate, traders say.

Indonesia

During the 1997 Asian financial crisis, the rupiah lost 80 percent of its value within months, sparking riots in Jakarta (and soon ending President Suharto's 32-year rule). The country's 100,000-rupiah note is currently worth $11.05.

Guinea

In 2002, the mineral-rich African country refused to implement reforms mandated by the International Monetary Fund. The foreign cash dried up and the central bank printed too much money. The 10,000 franc banknote is valued at approximately $2.33.

Iran

Iran's banknote with the highest denomination is the 50,000 rial, which is currently worth $5.35. After the revolution that took place in the country back in 1979, Iran's inflation rate varied around 15%. The continuously rising prices for oil had their impact on the country's inflation rate as well.

Sao Tome and Principe

This island nation located in Africa, in the Gulf of Guinea. The country is composed of two islands called: Sao Tome and Principe. The country's currency is entitled "dobra" and it most valued banknote is the 50,000 dobra note, which is worth about $3.47. The country exports mainly cocoa and thus Sao Tome and Principe is bound to highly unstable price of this good.