The top image on the page is a Golden Orb-weaver (Nephila edulis) as are a couple of Kevin's nice images. They are a different species than the huge tropical Golden Orb-weaver (Nephila pilipes) Bobj's post. There's also a pic of a Silver Orb-weaver (Leucauge granulata) the underside view and the St Andrew's Cross (Argiope spp. - most likely keyserlingi, but hard to tell from underneath). The St Andrew's get their name from both leg orientation and silk cross - the silk decoration is called a stabilimentum - it's function is still being studied but may involve the reflection of UV and subsequent attraction of prey insects to the web.
We've recently produced Australia's first spider ID app - Spidentify which you may find useful.
