DRI Status
If your hardware is not listed then it its 3D features are most likely not supported or work is in very early stages of development. Note that some vendor pages might be more up to date than chipset pages, and vice versa.
Links:
RadeonFeature (X.org wiki): Status of ATI/AMD Radeon 3D features among else
FeatureMatrix (outdated): Detailed summary of DRI driver features for a card and all supported cards
Independent Hardware Vendors
Chipsets