Both the Frontline and the Trenches (Baulkham Hills) that make up 'the Balkans' are excellent. The Frontline has something for everyone and the Trenches is a little more old skool featuring techy stuff and mantles galore.
The Fear Factory (North Epping) is also very good with many (pretty much all vertical/slabby) exciting problems, often requiring a cool head. Also as I said before, Lindfield is good fun too and an great place to waste a few hours (or years for some people).
I've written a piece on Sydney Bouldering featuring quite a few areas thats appearing in the forthcoming ROCK mag, so check it out.