>Is there any company which develops 3D accelerated graphics cards and has open source drivers for it ?
Yes. Matrox does, for example. Fairly nice ones too, though their cards aren't nearly as fast as Nvidia's and ATI's. ATI also puts some work into the open source drivers. I don't blame Nvidia for their decision to keep their drivers closed (and as it was stated above, they do have other peoples' IP to protect). They make good drivers... none of the OSS ones even come close performance-wise.
I support open source, I'm a kernel developer. I also support peoples' right to make choices. It's your property, do what you want with it, you know?