From that website if you want to run your current power supply I would go for this HD 7770:
Mwave.com.au - HIS Radeon HD 7770 iCooler Video Card - 1GB
I think your power supply could handle a slightly more powerful card, but the price jump to a gtx 650Ti or hd 7850 is way too substantial IMO.
If you are willing to upgrade your power supply then these are the 3 best deals I can see in your price range (hd 7870 and 2 gtx 660)
Mwave.com.au - ASUS Radeon HD 7870 DirectCU II 2GB Video Card Mwave.com.au - Gainward GeForce GTX 660 Golden Sample Video Card Mwave.com.au - Palit GeForce GTX 660 2GB Graphics Card