After spending a considerable amount of time glancing through the latest and greatest photos from the San Diego Zoo (courtesy of "geomorph") I am still convinced that no other zoo in North America is as impressive. I am the first to critique the older canyon enclosures, and there are still some scattered cages that seem somewhat out of place around the grounds, and Elephant Odyssey has definitely had mixed reviews, BUT in terms of both animal collection and overall quality of exhibitry the San Diego Zoo is as amazing as ever.
There are some other excellent zoos (Bronx, Columbus, Omaha, Woodland Park, Miami, etc) but how can they compete with: Ituri Forest, Monkey Trails and Forest Tales, Gorilla Tropics, Polar Bear Plunge, Giant Panda Research Station, Tiger River, Outback, Absolutely Apes, Reptile House, Reptile Mesa, East African Kopje, Sun Bear Forest and all of the magnificent aviaries scattered across the zoo. Wow.

I wonder how many zoos on the planet can even compare to San Diego's overall excellence? Toss in the Wild Animal Park and two of the all-time greatest zoos are within 30 minutes of each other.