For auld lang syne, ..high-end companies you really liked that are gone....

Fisher 

Fisher, Sherwood, Scott and Kenwood. These were the first "High End" receivers I saw upon entering Allied Radio store on South Western Ave in Chicago (around 1967). Kenwood is the only one still in business and it looks like they've stopped making Home Audio.

Dual, I use a 1229 idler driven turntable every day with a Grace 747 tonearm, it’s amazing. 

Advent, for their excellent speakers and cassette deck.  I still use a 201A cassette deck.  I think they have the best midrange of any cassette deck ever.
 
EPI, excellent speakers all of them pre 1980.

Nakamichi, loved the 1000, but the model 500 was my favorite.  That focus gap tape head was incredible!

The original Altec Lansing, they made of the best sounding speakers ever.

The original JBL,  same as above.

Phase Linear,  some of the best sound I’ve ever heard has been from Phase.  I love their amps.

Ariston, the original LP12.  Nice table.

Empire, great turntables and cartridges.

SUMO, GAS,  James made great amps and preamps. 
Harman Kardon  Citation, Pre 1980.  There was a time when this was spoken of in the same line as McIntosh, Audio Research and Threshold.

GRACE, excellent tonearms  and cartridges.

Counter Point, wonderful preamps and power amps 

Marantz pre 1975

Sansui pre 1978

Garrad 

Acoustic Research, that AR9 can still compete today.

KLH, the 9’s sounded fantastic if you could find an amp to drive them.

Apogee, loved there speakers.  Same as above.

Thanks for making me flash back! 
N

Here's my candidates, some are closed, some are brand-engineered into oblivion: 


Proton (screwed by Circuit City, run into the ground by their parent company, and gave up on having any presence in the USA)

Sumo (long gone - James Bongiorno was an audio genius, but not so good in business) 

AR turntables (Acoustic Research is just a name now, on bluetooth speakers, I think)

dbx used to make some really amazing hifi gear. Not just EQs and noise reduction stuff, but amps, preamps, CD players, even speakers. BSR and successive owners wrecked that. 

Superphon (Stan Warren was a freaking mad scientist, but like Bongiorno and even Nikola Tesla, not good in business. All he cared about was the next cool design, but any repairs and upgrades people needed, well, check back in about 5 years.)

@arichison - you posted some good ones. Let me add a couple of comments to your list if I may: 

ADS, and the a/d/s car equipment (probably the best amps ever made for the mobile environment, IMO) got bought out and leveled by DEI, didn't they? That group has wrecked quite a few original brands.

Nakamichi used to just exude an aura of awesomeness, but missed the digital revolution. Sad because they'd probably own the whole retro hifi movement currently happening. Now, Nakamichi is nothing more than a name owned by a Chinese company, and they turn out middle of the road home theater. Whomever owns the rights to the name for the mobile audio market seems to be putting out interesting stuff though.

Hafler, along with Acoustat, wrecked by Rockford Fosgate. Now they're yet another name, owned by some company up in the PNW. If you don't have schematics for any gear you own that was produced after the Hafler kit era ended, good luck with having that stuff fixed. 

@whatjd , I know this thread is a bit dated, but Straightwire remains in business.

Dunlavy Audio Lab
Oppo
Thiel Audio