Which countries have more than one official currency?

I don't know of any countries that have more than one official currency, at least not at the same time.

For a time, two currencies may be legal tender in a country if the currency has recently been changed - the former currency may remain in legal use for an overlap period even though it has ceased to be the official currency.

Some countries also officially accept that transactions may be made in a particular foreign currency as well as their own - se for example El Salvador and Panama which officially recognise the US Dollar as a legitimate currency in their jurisdiction even though they do each have their own official currency.

More commonly, it can be the unofficial local practice to accept payment offered in another currency as well as the official one - this is especially common in border or tourist areas or in countries where the local currency is not very stable.

I think you forget that Serbia-Montenegro (which is one country) has two official currencies, Yugoslav dinar in Serbia and euro in Montenegro.

I think you might be technically correct, author, though Montenegro severed its economy from federal control and from Serbia during the Milosevic era and continues to maintain its own separate central bank, collects entirely separate customs tariffs, and manages its own budget. In economic terms therefore the two are entirely distinct.

I think that Cambodia might have two currencies, the Riel and the $US. Also, Cuba does have two currencies in circulation, one for locals and one used primarily for foreigners, though locals use the foreign based currency too at more expensive restaurants, better shopping, etc.

Aside from numerous (mainly British) dependencies that recognise the local currency as well as the mother state's (e.g. the Channel Islands each have their own pound as well as the British one), there are a number of independent countries that recognise two or more currencies at once, as shown at https://en.wikipedia.org/wiki/List_of_circulating_currencies. Examples include Brunei and Singapore recognising each other's dollars, the South African rand being accepted together with the local dollar in Namibia and loti in Lesotho, and the current prize winner, Zimbabwe, which accepts the Botswana pula, British pound, Euro, South African rand,
United States dollar, and Zimbabwean dollar. Zimbabwe's own very weak currency situation gives an example of what led several states to abandon their own currency altogether, adopting another country's "stronger" currency- e.g. Ecuador, East Timor.

Several independent countries (Pacific islands) use the Australian (or US or NZ) dollar in commerce, but mint their own currencies commemoratively, like Kiribati, Nauru and Tuvalu.
Cambodia has just one currency, the riel.