Australian magpies, Gymnorhina tibicen, are larger, sleeker and more predatory-looking than their European counterpart. They are about 45 cm long, standing tall on surprisingly long, black, athletic looking legs that enable a very arrogant looking strutting gait along the ground. The beak is long and knife-like, with a black tip that fades to pale grey towards the body. The eyes are dark red with a round black pupil. The body is shiny black, except for a large white cowl over the back of the neck and shoulders, and smaller white patches on the leading edge of the wing and the rump.
In the air they are agile, flying quietly with fairly rapid beating of the wings. Their most infamous aerial manauver is the breeding season dive-bombing of any passing biped, as has been mentioned by FishHead. They drop from 40 feet up at high speed, aiming their rather evil looking beak at the back of the intruder's head. I have vague memories of being told as a small child that wearing an overturned 1-litre plastic ice cream tub with some eyes painted on the back on your head would deter them.
Their call is highly distinctive, with a long, burbling, liquid carol used to advertise their territorial interests, one of the most attractive bird calls of the Australian bush. Fledgling magpies are slightly less pleasurable to the ear. They follow their parents for several months after leaving the nest, slightly thinner and greyer than the adults. The parents will stay close together and forage for food while the baby hops along awkwardly behind, making a constant nagging high pitched nasal-sounding call eerily reminiscent of the noises made by irritable whining human toddlers. An interesting illustration of convergent evolution in action.
They're extremely common throughout much of the country, along the east coast to the south but tending further inland further north, and extending all the way into Westen Australia. Far northern and western birds have slightly different plumage to the eastern variety described here, but are the same species. They breed in October and November, laying one to six eggs in a nest in a high tree lined with feathers. The offspring mature extremely slowly, taking years to reach sexual maturity.