So far as I can figure out, during my travels I have been to the most northern, southern, eastern, western and highest points in Australia, that it is possible to ride to without leaving sealed roads.
Northern - Lee Point, just out of Darwin
Southern Mainland - Wilsons Prom
Southern Tassie - Southport
Eastern - Byron Bay Lighthouse (on my XJR1300)
Western - A spot on the road just north of Denham
Highest - Charlotte Pass
South West Corner - Cape Leeuwin
I've added "Head of the Bight", and Cabramurrra (Australia's highest town) which are probably other notable geographic milestones, and have been to Kulgera NT, which is as close to the Centre of Australia that sealed roads will take you. Unfortunately I didn't get a photo, so I must return one day.