The FreeBSD Foundation has been paying for porting the AMD KMS driver to Linux, after Intel KMS support came in FreeBSD 9.1. (NVIDIA/Nouveau support isn't too much of a concern since NVIDIA provides its high-quality proprietary driver already for FreeBSD.)
Progress has been good on this port of the Radeon DRM/KMS driver from the Linux 3.8 kernel to FreeBSD head. A status update was shared on Friday with the new progress being i2c calls and driver callbacks being fixed. On one of the FreeBSD test computers, the DVI connector is now correctly detected and functioning. The Radeon HD 5000 "Evergreen" series seems to be in best shape right now with basic functionality working, including the user-space AMD X.Org driver, RandR, and X-Video.
Porting the R600 Gallium3D driver to work on FreeBSD is also part of the project, but there it's still a work-in-progress. At least it's enough though for glxgears OpenGL demo to run at the moment.
The latest status on the Radeon graphics driver port to FreeBSD can be found via the FreeBSD.org Wiki.