This site has often been recommended by OzBargain members but I just got a chance to check it out. Here and here. They also will give you $10 off a booking of $300 or more until October 31 when you sign up.
lmtclub.com (this normally costs US$50 to join, but there are free membership codes floating around; has good rates for certain hotels, particularly in the US)
Best to play around with the site and see how it compares. Prices are in USD so comparisons are also in USD. My sample bookings (Nov 7/8):
Sydney Hilton
Hotelscombined - $331 AUD ($290 USD) -Hotelpronto
LMTClub $289 AUD (Converted) - $253.73USD
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Doubletree Metro NYC
Hotelscombined - $256.25 USD via Hotelsclick
LMTClub - $220.08
—
Palazzo Las Vegas
Hotelscombined $295 USD via Skoosh
LMTClub - $253.95 USD
Credit to MITM and Fatwallet. Fatwallet members don't recommend using it for flights, just hotels.
Shop around a bit. You might be able to do better with using coupons with hotel sites. Also check out the Travel wiki.
I recommend using them for attraction tickets if visiting the US. Was the cheapest for Disney and other tickets when I used them in January.