Panama, for example, is a popular retirement destination for a number of reasons. It's relatively close to the United States; the U.S. dollar is widely accepted and set at parity with the Panamanian balboa. The country offers a tropical coastline and mountains, allowing you to choose from various climates, and 20,000 to 30,000 U.S. expats are already living there.
Additionally, Panama offers the Panama Retirement visa, a permanent residency permit that gives import tax exemptions and discounts on things like utility bills, airline tickets, transportation, and health care services, among other things. Retirees can also enjoy retirement essentially free of taxes (such as federal income taxes) since the country does not tax foreign income.