I recently bought a X-fi for $99 (Cheapest I've seen it yet) at best buy, I listen to music 24/7 (yes I really do, even while sleeping) I absolutely love it! I've used the Audigy (original) and various M-Audio cards, but this is by far the best card I've used.
The CMSS-3D headphone and 2.1 works great, but not as good as a real 5.1 or 7.1 system. When I play CS:Source I can hear where every shot comes from and react accordingly.
The 24bit crystalizer is good, but still a gimmick IMO. It sounds wierd when enabled in games, so switching modes is necessary.