Visa to Panama
According to the U.S. bureau of consular affairs, U.S. tourists do not require visa for stays less than 180 days. There is USD$50/month fine for overstay. Immigration may grant extensions if requested before 180 days are complete.
Citizens of the U.K., Canada, EU, Australia and New Zealand have similar visa regime. For other countries please consult with your consular affairs or any other information source prior to your visit.