Care for the wide variety and uniquely plastic-sounding voices a general midi synth? This forum thread on electro-music.com details how you can make your own from an old Soundblaster daughter board -

This is a very simple project that will allow you to add a GM Midi Module to your sound creation arsenal. It can easily be completed in a single weekend including the panel.
What’s this module good for? It is a 24 voice/16 channel simultaneously available sound source. Each channel can access 127 different GM midi voices which cover most western instruments (classical, rock, jazz, folk, etc), some synth sounds, sound effects and a huge percussion kit (hardwired to channel 10). The voices respond to volume, velocity, pitchbend, modulation wheel, L-R pan, sustain pedal and a few other controllers. The more expensive soundcards will also cover reverb, chorus and other neat effects as well as more than 127 voice options.

The GM Voice on Electro-Music – Link #1, Link #2

Related:

Custom-built MIDI controller – Link