[vitaflo]

His Cynthcart for the C64 is much better and more versatile, I use it often with a midi keyboard to make chiptunes.

[Aldipower]

There is also the Mssiah cartridge, it even has a MIDI IN. Totally sick cartdrige. I integrated my C64 into my multi-instrumental MIDI setup driven by Cubase on an Atari ST with this. :-)