Our editors have moved to T play. 3D Sound has been a mixed bag every since it went mainstream with the introduction of Aureal's original Vortex chip. Since then, Creative, Sensaura, and ESS have jumped on to the raft. Even better has been the support. Still, the amount of games supporting Environmental Audio, Creative's 3D audio standard, is just as small as the amount backing A3D, Aureal's 3D solution.
Some games choose to support both, in hopes to gather customers from both sides of the tracks.
Other games like Red Storm's Rogue Spear, support EAX only because it is supposedly easier to implement. If you haven't already guessed, I'll be focusing on the first in the group, the X-Gamer.