lala, I would recommend either the Westin or the Sheraton on the Park. Both are very central in the CBD, but that means they generally don’t have fantastic views. The others mentioned by VK (Intercontinental, Park Hyatt, Four Seasons) do have fantastic views, but are more expensive and actually not situated quite as centrally. I’m not a fan of the Hilton; the rooms are tiny.
If the budget doesn’t stretch to any 5 stars, then perhaps look at some four stars such as the Four Points on Darling Harbour. All of the hotels listed have conference facilities.