The unit of currency is the Central African Franc (CFA), which is pegged to the West African Franc. Cash is king in Cameroon, especially in remote regions where it's the only way to pay – bring plenty of euros. Banks regularly refuse to change travellers cheques, and charge around 5% commission when they do. Moneychangers on the street in Douala and Yaoundé will change money at good rates and without taxes or commission, but there's always an element of risk to such transactions.
Most towns now have at least one ATM, which is always tied to the Visa network. Banks won't generally offer cash advances on credit cards. If you get stuck, Western Union has branches throughout Cameroon for international money transfers.
Express Exchange moneychangers change travellers cheques and US dollars cash; there are branches in many towns across the country.