I use my HTPC for gaming and movie watching and noise has always been a big concern for me. The 5770 with the Egg Cooler, version 2 of the card, is incredibly quiet. I was very impressed and surprised by just how little noise the card makes no matter it's stress level. It's silent TBH. I've got a Scythe Big Shuriken that I fitted with a Nactua 120mm fan, and a couple 80mm fans for exhaust, the 80mm fans are all I hear.
If you are picky about noise, i highly reccomend the 5770 as a consideration for low noise levels and solid performance. The card performs better than the 4890 and GTX260 in Metro 2033, in fact it is neck and neck with a GTX275 in this game with the new 10.3a's. So it's performance is improving from what orginal reviews showed in newer titles.