Visa requirements for Costa Rica change rapidly so check http://www.costarica-embassy.org/consular/travel/documents.htm for updates regarding passport requirements.
Currently citizens of the USA, Argentina, Brazil, Canada, Israel, Japan, Panama, Romania, South Korea, Uruguay, the UK, France and most other Western European countries do not need a visa for a 90-day stay. Citizens of Australia, Ireland, Iceland, India, Mexico, New Zealand, Russia, South Africa, Vatican City and most of Eastern Europe and Latin America can stay 30 days without a visa. If you do need a visa, it will cost approximately US$20 from a Costa Rican consulate. All foreign citizens entering Costa Rica must have a passport that is valid for at least six months after the date they enter the country. As of April 2007, citizens of the United States are required to have a valid passport for at least 30 days after the date they enter into the country.