Stereo SID - Internal Board for the Commodore 64
This is a great little device, made by Digital Audio Creations (http://digitalaudioconcepts.com/vanessa/hobbies/projects.html). It allows for two-channel SID music in demos or tunes with Stereo SID player - play up to 6 voices at a time! Similar to the SID Symphony cartridge, but this one mounts internally to your C64 - very cool!
Vanessa is always hard at work creating cool hardware for your Commodore computer.