As of February 21st 2008, the following currencies can be exchanged into Cuban Convertible Pesos (CUC) at Havana's international airport: US dollars, Canadian dollars, Euros, British Pounds, Swiss Francs and Mexican Pesos. The bureau de change is close to the exit and there are two locations on the arrivals hall. There is an addition one on the departures floor upstairs. 

The first thing to acknowledge regarding currency issues in Cuba is that all references to these in guide books published before November 8, 2004 are flawed. Prior to that date, the US dollar was readily accepted everywhere and was Cuba's second offical currency. However, since Nov 2004, US dollars are no longer circulated in Cuba. US dollars are subject to a tax (+10%) for changing them. Credit cards drawn on US banks (including affininty cards for non- US organizations that are administered by US banks) are not accepted. 

More information is available on the following page:

Cuban Money Exchange

Cuba has two currencies: the Cuban peso (CUP)  but tourists will be given Cuban Convertible Pesos (CUC) when they exchange their pounds, euros, Canadian dollars, yen or whatever on arrival. Note that tourists and Cubans alike can both use CUP or CUC. 1 CUC is worth 24 Cuban pesos. Where prices are quoted in local shops, the price is the same whether you’re a tourist or a local.

Money should only be changed at official exchange bureaux or banks to avoid scams confusing the two currencies. Do not exchange currency on the streets, even if you are offered a seemingly better deal.

The CUC is only exchangeable within Cuba. Its value is pegged to the dollar - 1CUC =  $1.00 since March 14th 2011. However, as stated above, you will pay a 10% tax upon changing US dollars into CUCs. This tax does not apply to other currencies, so if you are travelling from the US, you may have read advice in various places to change your dollars into another currency before travelling.  This only makes sense if you get a good rate to buy the other currency.  Do the math!

When changing CUCs back on departure note that once you have cleared security only $ US, $Canadian, GBP Sterling and euros will be available.

NB the Cuban authorities don't accept Scottish sterling notes.

There is no extra fee for using a credit card .  This has often been a misunderstanding, as a purchase in CUC is converted to US dollars using a factor of 1.03 x the price in CUC.  This is no different from the 3% currency exchange fee charged for cash exchanges.  A full explanation of this is available here:

Cuba: Currency and Credit Cards

While there are ATMs in Cuba, they may not be convenient to the hotels in many resort areas.  As well, the banks themselves are not that convenient to some hotels in these areas. Advice: Carry as much cash as you are comfortable with for changing over to CUC and take the opportunity to use a bankcard to obtain more money if it is convenient.