GPU coolers have gotten much quieter in the years since Nvidia strapped a Dustbuster to the GeForce FX 5800. If you want true silence, though, you've gotta go passive. Xbit labs has put together a good look at a trio of passively cooled graphics cards from Asus, Gigabyte, and PowerColor. All three draw from AMD's mid-range Radeon HD 6700 series, with Asus and Gigabyte using the 6770, and PowerColor opting for the 6750.
Obviously, the PowerColor card is the slowest of the bunch. The 6770s are pretty evenly matched on performance despite the fact that Asus clocks its memory 800MHz slower than Gigabyte. Personally, I'm more interested in how well the passive coolers work. Asus looks to have the best design, with its card's GPU hitting only 52°C under load—a full 15°C cooler than the Gigabyte card.
The Radeon HD 6770 should have few problems handling the latest games at resolutions up to 1080p, making it a good choice for silent desktops and home-theater PCs. Based on the sheer size of the coolers strapped to the Asus and Gigabyte cards, it seems unlikely we'll see substantially more powerful GPUs offered with passive cooling, at least in this generation.