Grey J.
Yelp
St. George Open Air Cinema is an extremely well-run open air cinema in the perfect possible location.
Tip: buy tickets well in advance. The tickets sell out, so book them once they go on sale.
Tip #2: get there early (say, two hours before the movie) and reserve your seats. Once you have "claimed" your seats, you do not have to stay in them, and you are free to roam the facilities for food, drink and socialising.
There are numerous seating options where you and friends/family can get drinks and food before the movie starts. It's great to make a whole evening out of it.
Another reason to get there early is for the photos. On one side, you have the Opera House and Harbour Bridge. On the other you have the CBD. Get there in time to take some photos before the sun goes down.
Once the sun goes down, the screen comes up and the movie starts. I often found myself paying attention to the surroundings more than the movie itself. That may be because I was watching Star Wars, a series I have never been particularly interested in, but I still had a great time because of the venue.
It's not a cheap night out, though. Between the cost of the ticket, dinner, and a few drinks, you can expect to pay ~$70/person. But it's worth it.