Sissy Crag is the premier bouldering area in Sydney. It's all overhanging (up to about 45 degrees) and features about a hundred individual problems ranging from V1 to V10+. There is a new guide available from most climbing stores and gyms called "The Sissy Crag Menu".
The crag faces due west, and isn't very shady, so summer mornings and winter afternoons are the time to be here. Sissy Crag also seeps very badly after rain, so give it a miss if there's been much rain in the previous week. It usually remains dry for about 2 hours in heavy rain, before water starts running down the walls and onto the problems (see for a photo taken during pouring rain).
There are also about half a dozen routes (from grade 22 up), but I've never seen anyone doing any of them, so I can't comment on their quality.
The guide for the area is the newly published Sun, Surf and Sandstone online guide book. This crag is described here.