Just published--"Snakes of Costa Rica" by Alejandro Solorzano--outstanding book with great color pics. Here's a link:

http://www.eaglemountainpublishing.com/

There are some other books as well, such as Jay Savage's definitive reference book on all Costa Rican herps, and Twan Leenders field guide, both of which are well done.

Cheers,

Bob Hansen