First thoughts:
- Lake Atitlán, Guatemala
- Antigua Guatemala
- Osa Peninsula, CR
- Bocas del Toro, Panamá
Lots more ideas when I've thought some more.
PS: on the way to Central America, if you're planning the time:
- Cantona, USM
-Yucatan Peninsula, USM
- Merida, USM
- Quintana Roo coast, USM
- Chichen Itza, USM