Musical inspirations behind Doom's music

Much of Doom's soundtrack is inspired by early '90s heavy metal music, and fans have long noted similarities between tracks from Doom's soundtrack and popular heavy metal songs. A well-known page on Doomworld titled Bobby Prince is a Filthy Thief details some of the more obvious similarities.

It is known that in developing Doom's music, Bobby Prince had a small collection of heavy metal CDs given to him by John Romero that were being used as inspiration for covers. In 2007, some of Doom's unused music tracks were released by John Romero, and metadata comments in these files name the tracks that inspired them. Using available data it is possible to build up a map of what was likely to have been in the collection used by Prince.

Definites
The following albums were definitely used as inspiration for Doom's music; this is substantiated by evidence from the metadata comments in the unused music tracks:

Alice In Chains - Dirt
 * Released September 1992. Referenced in metadata in seven different MIDI files.
 * Most tracks weren't used but "Them Bones" was used for "Bye-Bye American Pie", heard in Barrels o' Fun.
 * "Angry Chair" was also used for "Adrian's Asleep" in Bloodfalls.

Alice In Chains - Facelift
 * Released August 1990. Referenced in metadata in two MIDI files.
 * None of the tracks were used in Doom.
 * Though very different, "We Die Young" may have been the basis for "Hiding the Secrets", heard in Military Base. The percussion in D_E1M9.mus is nearly identical to that of that in un19.mid, and both tracks generally sound very similar to one another, especially since both add a supporting calliope later in the track.

Slayer - South Of Heaven
 * Released July 1988. Referenced in metadata in one MIDI file (un48.mid), though another file is also a cover of a track from this album (un52.mid).
 * "Behind The Crooked Cross" was used for "Deep Into The Code", heard in Pandemonium.
 * "South of Heaven" was used for "Shawn's Got The Shotgun" heard in Dead Simple,  The Citadel, and  The Living End.

Soundgarden - Badmotorfinger
 * Released October 1991. Metadata in four MIDI files reference two songs from this album, the first two tracks from the album.
 * "Outshined" was used for "Donna to the Rescue", heard in Slough of Despair and  Perfect Hatred.

Stone Temple Pilots - Core
 * Released September 1992. Metadata in two MIDI files reference tracks from this album (the first two tracks).
 * "Sex Type Thing" inspired "Into Sandy's City", heard in The Pit.

AC/DC - Big Gun (single) or Last Action Hero soundtrack
 * "Big Gun" is referenced in the metadata in one MIDI file (un44.mid); the single was released June 1993.
 * The song was used as inspiration for "I Sawed The Demons", heard in Deimos Anomaly.
 * Romero might have had the single, but it's equally plausible that he had the Last Action Hero soundtrack, which consisted primarily of songs by heavy metal bands that would have fit with the rest of the collection here.

Speculative
The following albums are not referenced in metadata comments. However, in each case, there are strong similarities to Doom's music tracks.

Pantera - Vulgar Display of Power
 * Released February 1992. Not referenced in metadata, though multiple Doom music tracks are inspired by tracks off this album:
 * "Rise" inspired "Kitchen Ace (and Taking Names)", heard in Command Control.
 * "Mouth for War" inspired the untitled song used in Fortress of Mystery and  Hell Keep.
 * "This Love" inspired "Waiting for Romero to Play" heard in The Courtyard /  The Abandoned Mines.
 * "Walk" inspired un51.mid from the unused music collection.

S.O.D. - Speak English or Die
 * Not referenced in metadata, but several of the unused MIDI tracks bear a strong resemblance to tracks off this album: specifically the songs "Pi Alpha Nu", "Milano Mosh" and "Speak English or Die"
 * The track "Sargent D & the S.O.D." was likely used as inspiration for "Facing the Spider" used in Dis.

Black Sabbath - Dehumanizer
 * Released June 1992. Not referenced in metadata.
 * "After all (the dead)" clearly inspired "The Demon's Dead" used in Refueling Base and  Suburbs.