I guess I'll put in my own suggestions for those looking for rare and/or large hoof-stock collections.
Firstly, my local zoo, the Cincinnati Zoo. The Cincinnati Zoo is pretty good hoof-stock wise. They have many rare species. They don't have the largest collection, though it is still pretty good compared to some others.Wildlife Canyon is wonderful. Sichuan Takins, Slender-horn Gazelles, Przewalski's Horses, and Sumatran Rhinoceroses all share side-by-side yards. The only disappointing part of Wildlife Canyon is that they have a yard that is home to a single Domestic Bactrian Camel, that could be held by another rarer endangered species. It'd be great if they could move him to the children's zoo. He's really sweet and looks kinda lonely in the yard all by himself. He'd be a great addition to a yard in the renovated children's zoo, but no so much the rare animal yards. As well they have and extensive collection of Red River Hogs. I love RRH's and all, but you see them every where. I'd really like to see the zoo get a rarer species of hog. Also, there is a yard for Bennett's Wallaby and Emus. This was the former Tufted Deer and before that Zebra Duiker yard. Flamingo Cove is home to Mountain Bongos, Yellow-backed Duikers, Okapis, and Grevy's Zebras, along with African waterfowl. Of course there is also Rhino Reserve with Black and Indian Rhinoceroses and Giraffe Ridge with Masai Giraffes. Their children's zoo has some interesting animals for a children's zoo. Besides the basic Nigerian Dwarf Goats, there are Dexter Cattle, Pot-bellied Pigs and Jacob's Sheep. In the next few years an African Savannah exhibit will be built and hopefully some new, interesting hoof-stock species will be joing the Giant Eland herd.
Second, is The Wilds. The Wilds is a 10,000 acre wild animal park outside of Canton, Ohio. The Wilds focuses mainly on endangered hoof stock species but in the past few years they have brought in several endangered medium-sized carnivores, Cheetahs, Dholes, and African Wild Dogs. The habitats for the animals at The Wilds are massive and very naturalistic. As well, the animals are kept in very large numbers. You will see herds of animals instead of just a few like you'd see in a standard zoo. The species include, American Bison, Pere David's Deer, Persian Onager, Wild Bactrian Camel According to the tour guides any ways), Masai Giraffe, Reticulated Giraffe, Baringo Giraffe, Indian Rhinoceros, Southern White Rhinoceros, Sichuan Takin, Indochinese Sika Deer, Central Chinese Goral, Przewalski's Wild Horse, Banteng, Fringe-eared Oryx, Bactrian Deer, Scimitar-horned Oryx, Common Sable Antelope, Common Eland, Grevy's Zebra, and Burmese Brow-antlered Deer.
Hopefully when Columbus's 70 acre African Savannah opens I will have another collection to write about.