The Sydney Festival: http://www.sydneyfestival.org.au/2010/ The link for 'free' has links to free things. The activities are in Hyde Park, the Domain, Macquarie St, Martin Place, and Cheifly Square.
Apologies: G3B also have made a GREAT video, singing 'Last Christmas'. Unfortunately the video was damaged and cannot be shown. we will keep working on this, but it seems we cannot put it up. Many apologies for this!