Lived in Bondi which is on the south side of the harbour and will probably take you <1 hour to get there.
Spent a lot of time standing on the rocks at the northern end of Bondi beach. Sun sets at 90 degrees to the waves crashing against the rocks and it's great at blue hour especially when the swell is high. Check
http://www.coastalwatch.com for wave height info. Tip: wet rocks are wet for a reason.
Watsons Bay, a few kms north of Bondi, faces the city and is great when the sun is setting behind the skyscrapers. Great places to eat there too.
Didn't spend much time north of the harbour but have a search on Flickr.
Apologies for pic quality as these were literally the first pics I took with a DSLR