I've done searches on "visualization" and the likes here, but only found a couple of questions about this -- none of which were actually answered -- and most of them over a year and a half old.

Besides 'PhonoVis' (I think that was the name of it), is there ANYthing out there that has a "Geiss"-style look? ("Milkdrop" would be better!!)

Just asking. I can't seem to find anything.

"Congratulations, Boots. Your robot is now self-aware. You're a daddy now." -- Dr. Rho Bowman

Yes there are players that support simple visualisation, the one that springs instantly to mind is Pocket Player which can even do fullscreen vis rendering, however they are limited to 2D vis only.

3D visualizers like Geiss and Milkdrop require a hefty amount of computing power and since 3D acceleration is only available in a very limited number of PDAs (your x50v is one of them BTW) the market for such a feature is limited.