We've always stayed in serviced (self-catering) apartments. If you like the Darling Harbour area you could try Southern Cross on Harbour but it is getting a little worn around the edges, but the price is right (A$140 for 1BR, last I checked.) The Southern Cross Apartments (now Trendwest) have undergone some refurbishment and have improved, or so I hear, at the corner of Goulbourn at Wentworth, for about the same price.