I've read that a yellow fever vaccination will be required for entering countries after visiting Bolivia, Colombia, Ecuador, French Guiana, Peru, or Venezuela in the last 90 days. I haven't gotten far enough to confirm what countries will require this but I have gotten the vaccination and thought I would share a web site with you to find a local clinic in the US to get one.
http://wwwn.cdc.gov/travel/yellow-fever ... earch.aspx