intel
Intel just released publicly the full technical informations and hardware specifications of their unified Shader Model 4 class i965 and G35 chipsets and graphics processor. These specifications concern all the GPU parts (2D, 3D and video encoding and decoding) and will allow third party open source drivers development.
Among other things, it includes very detailed and interesting informations on graphics pipeline shaders hardware implementation, like hardware states, internal formats, rasterisation policies and threads batching. Even if Intel don’t provide the highest performance hardware, these specification are very interesting and gives a good idea on how this kind of hardware can work internally.

Full specifications can be found here: