I'm looking for a travel agency to help plan a trip to Costa Rica plus Belize and Panama. I'd like to plan a custom itinerary, not take a cruise, not be on a group tour. Any recommendations for a reputable agency?

Welcome to Fodors. Do you have some specific concerns or complicating factors that make you feel a TA is required?

Most folks posting on here are more independent travelers and may use TAs in a few specific situations where one might be needed, but mostly plan things in their own. If you provide more info -- like when, for how long, how many people, what sorts of things you want to see and do, Fodorites can help you fill in the blanks.

Condé Nast Traveler magazine has a list of travel specialists for various countries and regions.
I use a travel planner when we go to Southern Africa and could not have had such marvelous visits without her help, I'm sure.
But Costa Rica, Belize, etc are pretty easy to plan, so... Just make sure the "agent" has been there many times and has good knowledge of the countries you want to visit.

That last sentence above!! Too many crazy stories of what a "travel agent" has arranged or suggested, when they clearly are not personally familiar with the places you want to go. Make sure you find someone who truly has lots of experience with Central America.

Also agree with janisj... mostly Fodor's is a forum of self-planners.

WELCOME! and hope others have some good ideas for you.