Here are a few more brands that I believe are gone that weren't on the list. Please update/correct if possible:
Amber (amplifiers)
Ariston (turntables, amps)
SWTP (Southwest Technical Products) Maker of Tigersaurus amps and others
www.swtpc.com for some info
Forte (less expensive amp line from Nelson Pass)
Loranger (Loran tape. I think Loranger is still around, though)
Soundcraftsmen (amps)
Coral (Japanese cartridges, OEM for many)
Lafayette Radio & Electronics (USA retailer with their own line)
Olson Electronics (USA retailer with their own line)
Sonographe & Motif (other lines from Conrad-Johnson)
Hafler (still has a website,
http://www.hafler.com/ but they're done producing product)
Utah (speakers)
Oasis turntable (not sure who made it, but Polk marketed it in the '70s)
Cizek (speakers)
Allison Acoustics (speakers)
3D Acoustics (speakers)
Electro Research (electronics)
Mura (headphones)
Precept (cartridges, by Audio-Technica)
Win Labs (phono cartridges)
Acculab (speaker brand from RTR)
RTR (speakers)
Acoustat (speakers, but maybe this counts?
http://www.acoustat.com.cn)
Counterpoint (electronics,
www.altavistaaudio.com for upgrades/repairs, and
http://www.counterpointaudio.com/ for an unauthorized Chinese knockoff)
Apt (electronics, started by Tom Holman)
This list could go on nearly ad infinitum, sadly. Just open any older annual product directory issue from Audio Magazine (gone, too), High Fidelity or Stereo Review (both morphed) or Stereophile to see more. Sigh...while some went away for good reason, some didn't.
Dave