I thought the Zimbabwean dollar was abandoned, and foreign currencies are now in legal use there. The Vietnamese D*ong has to be one of the least valued currencies in the world. According to Oanda's currency calculator, there are currently 19,000 to 1 US dollar. I don't know if there are any less valuable than that.
One billion Zimbabe Dollars (1000 million Zimbabwe Dollars) is worth about 8 US cents.
Yeah - I'm Trillionaire.
-- Best wishes - Majikthise.