Pied Imperial Pigeon, National Aviary, Pittsburgh, PA
Pittsburgh is blessed with a small but intensely friendly aviary (which received its honorary "national" status through an act of Congress). Like most zoos, it is set up to appeal to youngsters, though it also does serious conservation work. Of particular appeal, regular hand feeding opportunities in its two free flight areas. You really get to interact with these birds.
Some favorites: The Hamerkop (maker of enormous nests, and apparently thriving in the wild). Here's a close-up. Below, the hamerkop is hanging with a blue-bellied roller. What an attractive bird, that roller. Here are some other shots.
Also featured during the hand-feeding program: a family of golden-breasted starlings (probably the most assertive feeders). See the bird's amazing iridescence below: And I was also fond of this white-headed wattled lapwing who was constantly on guard against invaders of its fountain territory. This noisy green woodhoopoe managed to sneak in (though not for long).
The free flight areas are a bird photographer's dream, with amazing birds and unobstructed views (except for vegetation, as in the case of otherwise gorgeous black-headed woodpecker).