Azimer's Audio Plugin (0.56 WIP 1): One of the best SPU plugins developed by Apollo author, Azimer.

Azimer's Audio Plugin (0.56 WIP 2): A new WIP

Azimer's LLE Audio (0.50 beta 1): Another of Azimer's SPU and again it is very respectably programmed.

TR64 Audio (0.1): The TR64 Audio plugin developed by the TR64 team.

zilmar's Basic Audio Plugin (0.1): Very basic example plugin by zilmar. Emulates only the most basic of functions and should only really be used by developers. Includes sourcecode.

zilmar's No Sound Plugin (0.1): If your system is not very good or if you do not have a sound card, you may want to try this plugin. It does not process any sound emulation, and so allows more CPU power to be used for other things. Includes sourcecode.