The Creative X-Fi driver for the Advanced Linux Sound Architecture has improved a fair amount over the past few months and is certainly better than Creative's binary driver mess before they gave into open-source.
The CMI8788 Oxygen driver (used by sound cards like the Razer Barracuda AC-1) now includes support for HDAV S/PDIF inputs and when it comes to sound cards now works with the ASUS Xonar Essence ST. Another driver used by many Linux users is the HDA codec driver, which now supports many new notebooks and other sound devices. The HDA Intel driver also supports a new AMD HD audio device. On top of this, the USB audio support for ALSA has received numerous improvements in ALSA 1.0.21.
The lengthy change-log listing all of the work that has went into ALSA 1.0.21 can be read at alsa-project.org. Beyond the ALSA drivers, the ALSA library, utilities, tools, plug-ins, and PyALSA have all been updated to a version 1.0.21 status. These Linux sound driver updates come with optimal timing for getting into the Linux 2.6.32 kernel, with the merge window opening in a week or two.