Jaguars are arguably the most famous Central America mammal (well, besides monkeys), and also one of the most elusive. The big cats resemble the leopards of Asia and Africa, but are typically larger and more muscular, and the rosettes on their coat are usually larger and fewer in number. They're solitary in nature, and tend to stalk their prey instead of chase it. For obvious reasons, the jaguar has been used as a symbol of strength and power for centuries in Mayan culture.
Even black jaguars (called melanistic jaguars, or black panthers) have spots, visible in certain lighting or upon closer examination.
Where you can find them:
Dense forests all over Central America. Although glimpsing a jaguar is very unlikely, if you're determined, Belize's Cockscomb Basin Jaguar Preserve is a good bet (I've seen jaguar prints there, though no actual cats).