If you're in Sydney, couldn't you have a frangipani tree...?? If you have an older style house, they look fantastic against a bare bit of wall and smell divine in summer! Not so good for shade as such, but if you already have a shade tree and need another to fill a space, they are lovely.

Another personal favorite which could grow quite big, BUT you could keep it trimmed smaller, is a Jacaranda. We've got one out front, right under the powerlines, but ever so often the power company comes past and lops off the top growth, and it still looks lovely.

Final suggestion - again, not a shade tree, but would do as a second thing to a big shade tree, is to consider planting a stand of silver birches. They are pretty all year round, lacy foliage, yellow in autumn and silvery-white bark in winter - if you plant several together in a stand they don't get very big.