The Toronto zoo has a great Australasian exhibit. There are kangaroos, tree kangaroos, wallabies, echidnas, wombats, sugar gliders, lots of birds and reptiles like Komodo dragons, and a Great Barrier Reef area with sharks, seahorses, jellyfish, and more. I know it's not in the US but I thought it should still be mentioned. Another small Australian exhibit that I have seen was at zoo Miami. It included koalas, tree kangaroos, emus, singing dogs, and crocodile monitors. Although it wasn't as big as Toronto's, it was still a decent exhibit area. Other good Australian exhibits that I haven't been to are at the Cleveland zoo and the Fort Wayne zoo.
Sedgwick County zoo's Australia exhibit is in my opinion fantastic. Dallas and Fort Worth both have sub-par Australia complexes.
I'll support ArcticWolf's statement above - I'd list Ft. Wayne and Cleveland as the two best Australian exhibits I've been to. Re: Ft. Wayne - I love the the 'look' of Ft. Wayne's Aussie central courtyard plaza, the idea of 'Australian Welcome Center,' nocturnal exhibit and the gentle river ride that takes visitors past both their dingo and kangaroo exhibit. The crown jewel may be their two large-tank aquarium dedicated to the Great Barrier Reef and sharks. (I believe there are small jellyfish tank in their, as well.) Re: Cleveland - CMZ's Reinberger Homestead very-much reminds of one of the enclosures in Taronga's Backyard-to-Bush area. The indoor-outdoor koala exhibit is nice and the interactive Yagga tree is great for the kids to burn-off energy. They also recently shifted their New Guinea Singing Dog exhibit to one focusing upon dingoes (acquired from, ironically, the Ft. Wayne). Kudos also go to San Diego's koala exhibit and Columbus' nocturnal house, which opens with an Aussie pub theme...
Probably the best-themed Australian exhibit I've seen is at Granby Zoo, which has Bennett's wallabies, emus, gray kangaroos, sulpher-crested cockatoos, and black swans, which does jazz up your usual walkthrough by giving it a highway travelling theme, such as the pavement having yellow lines and the emu being themed around a gas station. The nearby aquarium's a nice touch too. EDIT: I will, however, give Toronto Zoo as the better exhibit overall, as it has some rare species even outside Australia, and has some good theming and exhibits itself, such as its komodo dragon exhibit.
Seeing as this thread has been revived I'll give my thoughts as to what the best United States Australian exhibit is. My favorite two are the Brookfield Zoo (decently sized building with herps, Wombats, Echidnas and Bats with large outside paddocks for Emus and Kangaroos) and the San Diego Zoo (loads of birds, along with rarities such as Tasmanian Devils and Koalas). Outside of the U.S but the Toronto Zoo has a very good Australian house with large aviaries, lots of herps, wombats and a well-sized paddock for Kangaroos and Wallabies.
