At least for U.S. Zoochatters...
Fish
Mangarahara cichlid- Toronto
Reptiles
Tzabcan rattlesnake- Crococun (could be more common in the private sector in the U.S., I'm not sure however)
Yellow-lipped sea krait- Toledo
Birds
Resplendent quetzal- Xcaret
White-headed vulture- Toledo
Mammals
Commerson's dolphin- Aquatica Orlando
Guatemalan black howler- Xcaret
Yucatan brocket deer- Xcaret
I've seen other species that many probably haven't seen, however I was either too young to remember or was before I kept track of the species I've seen (ex. finless porpoise, harp seal, etc).