MadShrimps tested and compared 8 different VGA coolers from Zalman, Gigabyte, Vantec, Coolermaster, ZEROTherm, Arctic Cooling and Titan. The models range from completely passive no-noise solutions to multi heat pipes equipped cooling monsters. Here's an excerpt:
Let's analyze the data gathered, the stock NVIDIA cooling does a poor job at keeping the 7900 GT running cool, at 750C it's running hot and at 60+dBA it's very loud too. The only other cooling solution which surpasses the stock cooling in the noise department is at the other end of the performance chart.

- Gigabyte V-Power: this 7900 GTX cooler look-a-like does a formidable job at cooling the 7900 GT, although at high speed the fan is quite noticeable, but performance is really good, only 470C (amazing 280C drop compared to stock) and ~52dBA. Reducing the fan speed makes the cooler silent, but you do get a +70C temperature penalty.

- Vantec IceberQ 6: the design of the IceberQ 6 is quite dated and it shows in the chart, at high fan speed the GPU is kept cool enough (-200C) at 550C, the fan is noticeable at ~51dBA. If we want silence, the low fan setting delivers, but temperature rises by 130C!

- Coolermaster CoolViva Z1: The CoolViva Z1 in complete passive mode performs on par with the stock NVIDIA cooling, minus the noise of course. A commendable effort, but not much room left for overclocking. If we speed up the rear case fan a bit noise increases only ~3dBA but temperature drops to a more comfortable level at 670C. But it's better to mount a silent fan on the Z1, with a silent 80mm the noise level is practically the same as with the speedier rear fan, but temperatures are now at ~550C mark! Setting the 80mm fan speed to high puts the Z1 into the higher performance part of the chart, the noise level is now ~51dBA and it's definitely noticeable, but temperatures drop another 60C to ~490C.

- Coolermaster CoolViva Pro: The fan of the Pro was only tested at one setting: full speed, because of compatibility issue connecting to a normal 3-pin fan speed controller. The Pro is noisy at full speed, at 53dBA is noticeable, temperature results are mediocre at best, 20C hotter than the quieter CoolViva Z1. We suspect that mounting pressure is the issue here.

- Arctic Cooling Accelero S1: The S1 doesn't fail to impress, no matter how you look at it. The performance in complete passive mode is stunning, 560C! Increasing rear case fan speed to 7v drops temperatures 60C to 500C under load. But as before, it's better to provide direct airflow to the S1, with the Turbo Module installed and running at low speed the noise level is at 42dBA, temperatures are at an amazing low of 44.50C. Increasing the Turbo Module speed to high increases noise to 46.7dBA making it faintly audible, but the expected performance increase is absent, only -10C. We suggest Arctic Cooling lowers the default speed of the Turbo Module when running at full speed, the extra airflow doesn't pay of. As a last test we mounted the 120mm 2900rpm fan and were not disappointed by the thermal performance of the S1, at 41.50C this 7900 GT was running 33.50C cooler! (at 73.7dBA it was also audible from two houses down the street, but who wants silence anyway, right? ;-) )

- ZEROTherm GX815: The biggest competitor of the GX815 when comparing design is the VF900 from Zalman, we can see from the results, that at high speed the newer GX815 falls between the VF900 running at high/low speed. We did not disable the temperature control of the fan, so depending on your ambient temperature and VGA card used the noise levels will differ. At 50.3dBA the GX815 was well audible; when we lowered the max voltage of the fan to 5v the GX815 become very quiet, performance was still ok at 54.50C, but it's bested by the performance/noise ratio of the VF900 (@low).

- Titan Twin Turbo: The Twin Turbo had quite a bit of high end competitors in this roundup, but it managed to perform respectfully, build for high airflow the TT does best with its fan running at full speed, generating ~48dBA it's noticeable but not too disturbing. Performance trails the V-Power unit from Gigabyte by only 0.50C, negligible. At low setting the TT bests the V-Power in both noise and temperature results, and does quiet well in the overall ranking.