May 2012 ,Ghana cedi is 2 to $, 2.5 to Euro and 3 to £. Many still use old pre revaluation cedis in pricing e.g. 'is one million [ 100 new ] = $50.To be safe say 'New Ghana'.ATM's are now widely found in the 10 major cities.

Ghana is more than happy to take your hard currency!   Forex bureaus accept USD, CAD, GBP, Euro, JPY and some of the Ecowas currencies.  Follow this link for current foreign exchage rates. Ghana Foreign Exchange Rates 

Here are some basic guidelines:

Cash and Foreign Exchange – Bring only cash  to exchange into cedis. There are forex bureaus everywhere in Accra, and many of the bigger hotels[ 5-10% penalty] such as La Palm, Labadi Beach, Golden Tulip, have forex bureaus as well.      Out of Accra and major cities any large market will have a money changer  . .CASH is king in to bring hard currency in larger [ they like $/euro 100's and uk£ 50's] denomination notes and use the wide spread forex offices to get the best rate.P.S. Always carry plenty of  ghc 1,2,5 and 10 notes ,often vendors/taxis dont have change [or claim not to ]

Traveler's Checks - There is debate about whether or not traveler's checks can be cashed in Accra. Research carefully and bring cash as a back up.

If they are accepted in Ghana, it is likely that the larger hotels that have Forex will likely take them, and the bigger Forex bureaus, as well.  Two important things you should be aware of, one is that your rate will be less[up to 10%] than if you use hard currency, and two, as you go out of Accra, you may encounter MUCH more trouble finding a place that will take your traveler's checks. TRY to avoid using traveler's checks in Ghana, they are a costly and tiresome way to carry money.   For a full list of banks operating in Ghana, follow this link Banks in Ghana .  

Credit Cards - One important note, before you leave home is to ALWAYS contact your bank or credit card company and tell them you wish to use your card in Ghana  There is a limit to how much you can withdraw at an ATM, and it is usually less than $100 (in local currency, of course). Don’t use them unless an absolute emergency. Credit card fraud abounds in West Africa. Not even in the big hotels should you consider using your credit card. Bring cash to pay for your purchases. For cash advances, it is safe to use your credit card at a bank, inside or at the ATM. 

If emergency funds are needed to be sent, there are many agencies set up for expat remittances -  in Europe and USA which use a PIN and ID system such as Unity Link in London and funds can be collected in any Ghanaian bank on the same day.