ATI Has Open-Source Drivers Too @ Phoronix
 

Since late last year the open-source Linux community has been
ecstatic about the growing progress made by the Nouveau developers.
Nouveau is an X.Org and FreeDesktop.org project for developing an
open-source 2D/3D display driver for NVIDIA graphics cards. With NVIDIA
Corporation not providing hardware specifications, this driver is being
written through reverse-engineering NVIDIA's binary display driver.
While the developers of Nouveau are making great strides and this driver
is taking shape, the open-source ATI driver must not be forgotten.

http://www.phoronix.com/vr.php?view=9730