What is the cheapest currency in the world?

As of March 22, 2012

US Dollar 1 = 20,850 Vietnam Dong

US Dollar 1 = 11, 335 Iranian Rial

US Dollar 1 = 7, 970 Laos (laotian kip)

US Dollar 1 = 4,000 Cambodian Riel

US Dollar 1 = 361.000 Zimbabwe Dollar