1. Squirrel monkey - Not only are they very common in zoos, but they would also add a monkey with a dragging or dangling tail. That would do wonders for modding of other monkeys. At this point, I don't particularly mind what species.
2. Spider monkey - Commonly-kept in captivity (much more common than howler monkeys, which I'm personally not massively enthused about) and very interesting animals to look at. Don't particularly mind what species it is, provided it is kept at least somewhat frequently.
3. Agouti - One of the most commonly-kept of South America's rodents, very suitable for mixing with other species and very nice to look at. Any of the following three species would be fine for me; Azara's, red-rumped or black-rumped.
4. Ring-tailed coati - Pretty commonly-kept in zoos and one of the most-wanted animals left for the game. Can also represent both rainforest and grassland biomes.
5. Scarlet ibis - Of the South American birds, this is probably one of my favoured choices (for a broader Americas pack, I would add the ocellated turkey and greater roadrunner). They shouldn't be too challenging to make from the flamingo, would add a brilliant flash of colour and represent a new bird group not in the game so far.
As for exhibit animals, I'd go for anything provided it can actually be kept in captivity - emerald tree boas, eyelash pit vipers, bushmasters, false water cobra, Andean milksnake, Peruvian bush anole, Amazon milk frog, Titicaca water frog, aquatic caecilian, more poison-dart frogs, crayola katydid, Surinam grasshopper, a species of praying mantis, headlight beetle - I wouldn't mind any of those just for starters.
