The value of a currency may be different depending on what you use for a 'value'. For example, the Japanese Yen may have a different 'value' if you are comparing it against the Euro or the US Dollar, for example.
Believe it or not, the smallest unit of currency (in terms of value of US dollars) is the Vietnamese Dong, at a value of 0.00005 Dollars per Dong.
Maybe the Zimbabwean dollar is counted differently, maybe/
moneycentral.msn.com has a cool currency converter which allows you to compare all current world currencies against a single currency, and presents it in a chart form.