Music Players featuring the dlMV Music Visualization Engine:

Quintessential Player - PC Freeware
QCD Homepage A slick full-featured and constantly improving player by Paul Quinn, features the Visual Plugin Fifth Trip by dl
QCD Visual Plugins Page don't miss the Retro Vis Pack by dl (Coders, grab the source, and also the PDK below)
Write your own Plugins! Check out the QCD Plugin Development Page and grab the QCD Plugin Development Kit. You'll find the header files and my technical document on dlMV to get you started.

dl's Homepage