When it comes to the C-Media Oxygen driver for the Razer Barracuda AC-1 and other high-end sound cards, the HT Omega "Claro Halo" sound card has been added and there's also a fix in this audio driver so the EEPROM on the ASUS Xonar D2/D2X doesn't get overwritten.
Some of the other changes include enhancements to dynamic audio power management, a horde of SoC layer improvements, and USB audio changes. Beyond the ALSA drivers there are also a number of changes to the ALSA library with version 1.0.19. New versions of the ALSA utilities, tools, firmware, and plug-ins have also been published.
While Creative Labs had allowed 4Front Technologies to create open-source X-Fi support in the Open Sound System nearly a year ago by releasing the needed APU specifications, there still is no Creative X-Fi support in ALSA 1.0.19. Creative Labs had even open-sourced their X-Fi driver back in November, but no code has yet to hit ALSA.
The list showing all of the many changes between ALSA 1.0.18 and 1.0.19 can be found on the ALSA Project Wiki. The latest packages to download can be obtained here.