Sydney harbour is very scenic area and it is really great place for lighthouses hunters :) Good way to see some of them is to take trip on Sydney Ferries from Sydney (main wharf is Circular Quay in the City) to Manly (suburb of Sydney).
First light on the way will be Fort Denison lighthouse, built in 1913 on the top of 19th century fort (all images below are clickable)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4559.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2928)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_5536.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2929)
Robertson's Point (1910) is next one on the port side just after Fort Denison.
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4545.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2946)
Next lighthouse is very simular to Robertson Point - Bradley's Head light:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4532.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2935)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4533.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2936)
Then to starboard of the ferry - Shark Island light:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4638.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2945)
In the middle of harbour two lighthouses constructed in the water. Red is Western Channel Pile Light:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4512.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2912)
And green - Eastern Channel Pile Light
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4506.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2911)
All these lights are quite small - no more than 8-9 meters of elevation. But in the gateway to harbour there are 2 more "advanced" lights. First is Hornby (South Head Lower) Lighthouse, oldest in the area (1858):
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4488.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2916)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4429.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2915)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_5468.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2917)
And MacQuarie (South Head Upper) Lighthouse (highest and most powerful - range is 25 nm), constructed 1883:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4414.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2914)
Additionally in Sydney you could find 2 lights in National Australian Maritime museum (Darling Harbour).
First is Cape Bowling Lighthouse (1874, rellocated here in 1987):
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4854.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2904)
And Lightship CLS-4 (Carpentaria) - she served from 1917 to 1987 in the Queensland:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4851.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2901)
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4973.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2902)
And the last one very unisial:
(http://www.lightphotos.net/photos/albums/userpics/10001/thumb_IMG_4433.JPG) (http://www.lightphotos.net/photos/displayimage.php?pid=2925)
Yes, you're right this is water tower. But additionaly it is included to the Admiralty list of lights as K2653 (red and white light, occulting every 3 seconds) :)