While it does not integrate directly with MC, Milkdrop3 is currently the best visualizer you can get IMO. In addition, it's free, open-source, and actively developed (latest version is from October 2023).
https://github.com/milkdrop2077/MilkDrop3If you ever used Milkdrop or Milkdrop2 with Winamp in the past and still have the *.milk files from those installs, they will work perfectly with Milkdrop3. You can also find bulk downloads of *.milk files. I downloaded one such zip file years ago that had 45,000 files in it, but it did have a lot of duplicates and a lot of duds (I have since culled that to approximately 12,000 files). Regardless, launching this spectacular visualizer as a standalone window makes it well worth downloading.
Perhaps with the future change in J River's ownership, integrating Milkdrop3 into MC and/or purchasing it outright might become a reality? I am crossing my fingers at least! I am also crossing my fingers new owners won't gut and destroy the best media player there is.
