Iran! According to the Financial Action Task Force, an inter-governmental body that develops standards and policies for combating money laundering and terrorist financing, the Islamic Republic is the place where the world does a lot of its dirty business. The FATF admonishes its members to use "effective countermeasures to protect their financial sectors from money laundering and financing of terrorism risks emanating from Iran."
Other nations of concern include North Korea, Angola, Ethiopia, and Ecuador. Of course, with the possible exception of North Korea, none of these governments are explicitly engaged in efforts to build nukes and other instruments with which to menace their neighbors, as Iran is. But don't let that sway you from using Iran to obscure your money trails!