If you're trying to book a stubborn hotel that doesn't want to accept any coupons ('Voucher not valid for this hotel'), you might want to give this one a try.
DCOAUD35 gives you $35 AUD off any booking over $500. However, you can use the equivalent U.S. code and get $35 USD off (~$50 AUD) with DCOUSD35.
Warning!!
Otel.com are slimy and charge fees to book with a credit card. They are also sneaky and will charge you in AUD, but process the payment in Turkey - so your credit/debit card could still be slugged with a foreign transaction fee. 28 Degrees, Bankwest Platinum, and Citibank Plus are the only cards I'd trust with this site.
The only reason I'm posting this is because, even with credit card fees, they ended up significantly cheaper for two Chinese hotels I booked recently. As usual, do your homework on Kayak, Trivago, HotelsCombined, SkyScanner - to make sure it's the best deal for your accommodation.
Don't forget your 4.80% cashback with CashRewards, but it's very likely they won't honour it with the coupon.
Honerable Mentions
Here's two other coupons which seemed to work even with stubborn hotels:
Hotels.com - AUWORLD - $40.00 off (min 2 nights, min $360 spend)
Webjet - WEBJETCHAT - 5% off
'Otel… Reminds me of 'Allo 'Allo…