I would wait for AMD's 7xxx. The 28nm manufacturing process increases performance per watt a lot, so you can expect lower heat GPUs at gtx570-580 speeds, than what the current generation has to offer.
Unfortunately, I expect custom-cooled cards start appearing later on. It's just that you can't find properly quiet 570/580 cards without expensive watercooling, heavy underclocking or reckless disregard for temperature...
Maybe there is one exception. The ASUS 6970, GTX570 and GTX580 cards with triple slot coolers. The huge heatsink would allow you to create a custom fan profile in afterburner to quiet the card down. But you need good airflow. Can you fit that in your case?