A Guide to Amphibians and Reptiles of Costa Rica
Twan Leenders
305 pages
Priceless

Ok, so it's priceless because it's out print, but if you can find it, buy it. This book is my absolute favorite field guide for Costa Rica and not because I know the author. Leenders' book is the original field guide for the country and is still (in my opinion) the best. Unlike Savage's 6 pound behemoth, this book easily fits in your daypack and makes identification easy. The photo array in the middle includes both scientific and common names as well as the applicable page numbers. His identification information and remarks are incredibly accessible and useful. He provides easy field identification techniques for almost every species; like methods for telling apart the traditionally tricky Eluetherodactylids. If you're going on vacation and want one book to take with you, this is it. It includes all of the common and some of the uncommon species you will encounter.

Although the asking price for this book is astronomical in the U.S. I have seen copies for sale in airports in Costa Rica and El Salvador and in book stores in Costa Rica for the original asking price ($25.00).