A year or so ago, also on a rental I went from Sydney, south through the Royal National Park and along to the great ocean drive. Great scenery and twistys.
I also went North of sydney, all along the northern beaches from manly to Palm beach.
And on the way back went through Bobbin Head, and then cut across to Galston Gorge. Some good hills and hairpins.
If you're willing to go further afield again. Take the old pacific highway north to Gosford then Terrigal or The Entrance.
Hope this give you some ideas!