Title says it all. Well almost. They need to push some air, but not be louder than around 16 dba. And my fan controller isn't making my current fans as quiet as I'd like; in fact they're the loudest in my system. Any price range. LED's are a plus.
Noctua has some excellent 80mm fans but they're rather pricey (although exceptionally quiet), and Enermax has some magnetic-barometric 80mm fans that should be really quiet as well. I've only seen the 120mm Enermax fans in action though, not the 80mm ones so I'm not speaking from experience there. Arctic Cooling also has some FDB 80mm fans out, those might be worth checking out.