In Sydney, get a Sydney Pass. We had unlimited travel on buses, including the two explorers (Sydney and Bondi), trains and ferries for A$110 each, allowing us to see what we wanted at our own pace.
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If you want to go a little further out, to Manly for instance, the green travelpass is only $43. Far better value than the rip-off tickets sold to tourists...
www.cityrail.info/fares/travelpass.jsp