Not long ago I stumbled upon this site:
Roland SC-55 Music Packs
I'm sure some of you guys know it, but I think it's still worth mentioning. The site's author, Brandon Blume a.k.a. MusicallyInspired, has recorded synthesized music from such classics as
Duke Nukem 3D,
Rise of the Triad and
Descent on a real Roland SC-55 board, resulting in high quality soundtracks in OGG, MP3 and FLAC formats. There's also a page with a brief summary of video game music media history too.
The full list of soundtracks currently available is as follows:
Duke Nukem 3D Atomic Edition (OGG)
Duke Nukem 3D Authorized Add-ons (OGG)
Rise of the Triad (OGG)
Shadow Warrior (OGG, MP3, FLAC)
Blood (OGG, MP3, FLAC)
Descent (OGG, MP3)
Descent II (OGG, MP3, FLAC)