I had purchased the Lonely Planet city map of Sydney, and this was the best thing I could have done for getting around. The map was very up to date, showed all the various modes of transportation, and where to get on and off, and had many of the city highlights pointed out. This made getting around painless and within the hour of getting there we were off and running!
One thing I loved about Sydney was that there were so many different types of maps available!! All of these should be available from your hotel lobby, but its great that you will never really be lost!!