So far, the only A3D supported game that has impressed me was Quake 3, but it has to be a REALLY old version of the game. I'm not sure exactly which versions...I know v1.0 works fine, and the demo works fine...a few newer revisions worked okay but had the stereo reversed. The Gold version seems to have had all of the A3D 2.0 support ripped out.
Edit: I'm skimming through the Q3A source code right now, and it looks like all of the A3D stuff is still in there, it's just commented out. I'm really tempted to try compiling this. Athough, when I was looking at different versions of the game before, it looked like some of the A3D information was hard-coded into the BSP maps, so I'm not sure how much good it would do. I could be wrong, however.