AnandTech takes a look at a bunch of low-end, but silent graphics cards:
All this leads us to today's topic: enter the Silent Graphics Card, a graphics card that is completely passively cooled, often using heat pipes and an oversized heatsink to eliminate the need for a fan to keep the GPU/memory cooled. The idea of a quiet or silent graphics card is appealing to many types of computer users, and many card manufacturers have realized this and are offering silent solutions. In the past, the only passively cooled video cards were slow entry level offerings. This is no longer true, and you can now get many mid range GPUs that offer reasonable performance without any noise output. The highest end GPU solutions are still all actively cooled, but if you're looking at any of the more affordable GPUs, you may be able to find a passively cooled alternative.