United Kingdom

American dollars can be exchanged to British pounds locally without much difficulty -- the lowest rates typically found from local post offices. Depending where in the UK you're visiting, finding a post office may be difficult and opening hours will vary. Something else to keep in mind here is the cost of withdrawal fees, which are taken by both your own bank and the local post office. That said, it's generally best to exchange your dollars to pounds before leaving the States. Even if you plan on paying most expenses with a credit card, it's recommended to keep a minimum of £50-100 on you for taxi rides, small boutique shop purchases and considering the must-see London flea markets where cash will be needed.

TIP: It's generally not a good idea to carry all your cash with you in the UK. Take advantage of your hotel room's safe.