DooM II music - MAP 3 and MAP 21 (OPL)
Of course, there are many other videos on youtube with the DOOM/DOOM2-OST, but they all use the MS-GS-Wavetable or other PCM-based synthesizer. This make the music sound "more real", but not Doom-like anymore.
"Skulltag" includes a great OPL-synthesizer which plays the music back "correctly" (our SoundBlaster-card in '95 sounded almost the same). "DosBox"s synth doesn't sound bad, but many instruments are just weird there xD