Important notice about traveling to Costa Rica:

As of January 8, 2007, passports will be required for all U.S. citizens traveling to or from the United States via air or sea, to or from Canada, Mexico, Central and South America, the Caribbean, and Bermuda.

Also, if you're flying out of Costa Rica, you will need to pay a departure tax of $26, payable by cash or credit card.  If you happen to be flying to/from the smaller San Jose Pavas Airport to get around the country, it is highly recommended to pay this tax while you're there rather than waiting in line to pay the tax at the main San Jose Santa Maria Airport since lines are significantly shorter (or non-existent) at Pavas.