Darter Anhinga melanogaster
These birds don't have water-repellant feathers. This means that after being in the water, they have to stand with their wings out to dry, like in the photo at left. But it also means they swim underwater really well. This is a fairly big bird that often just pokes its head out of the water - the rest being submerged. It gives them the appearance of a snake, which is why some people call them snake birds. They eat fish. More info here

Egret Ardea species
A very regal-looking bird with a crazy long skinny neck. I'll come right out and say these egrets look pretty much the same to me. Extremely beautiful, definitely, but hard to tell apart. In case you're wondering what I mean, there's the Great Egret and the Little Egret. And there's an intermediate egret called, (I swear this is true) the Intermediate Egret. Now, the Little Egret sometimes hangs around cattle, as does another type called the Cattle Egret. So I admit I'm not good with egrets, but at least I can tell them from the cattle. They eat fish and insects.

Maned Duck Chenonetta jubata
Also called the Wood Duck, that's the female on the left, and the male on the right. The male has a cute brown mane on the back of its head, while the female is more spotty underneath. This bird is just as comfortable on land and among trees, as long as there's water somewhere nearby. They feed on some types of grass and seeds, with a real taste for rice.

Eurasian Coot Fulicia atra
A few of these guys swimming around makes a pleasant, calming scene. But watch a whole lot of them and you're likely to end up with a facial tic. These black and white birds create large floating flocks in a manner which looks confusing to me, but which obviously makes a lot of sense to the coots. Almost exclusively vegetarian, when it comes to breeding time these birds sometimes forget to play nice with other species. They've even been known to kill the occasional duckling.

Musk Duck Biziura lobata
One strange-looking duck, this one. First of all, it often swims half-submerged. Second, the male has a large lobe of skin hanging under its bill. It distends it during courtship to look attractive to the female. Beauty in the eye of the beholder, I suppose. If you should ever find yourself close enough to one, you'll notice that the lobe has a strong musky smell. Thus the name. During courtship the male splashes water behind it during an impressive, noisy display. Sydney is unlikely to see this because it's apparently outside of its breeding range.

Hardhead Aythya australis
If it strikes you as being cruel to label this critter a 'Hardhead' then 'White-eyed duck' should also do it. Speaking of white eyes, the males have them while the females have brown eyes. Hardheads are good swimmers, both on the water and diving into it. They eat mainly water plants but also some critters like aquatic beetles and yabbies.

Masked Lapwing Vanellus miles
These critters used to be called Spur-winged plovers but their name was changed to stop confusing them with the spur-winged plovers of the nothern hemisphere (a different species). Like their (old) name suggests, they have a claw-like spur on each of their wings. You can see that claw on the enlarged version of the photo far left. They have a loud call which can sometimes be heard as they fly overhead at night. They hang around in places like parks and grassy areas where they feed on insects. These birds build a nest on the ground and defend their young by swooping at anything that comes close.