For currently active companies, producing high fidelity equipment:
1. Accuphase, by a clear country mile.
They have never deviated from producing the finest, best performing and luxurious Japanese product since their inception in the early 1970s. Their quality, support for old products, and guaranteed conservative specifications have set the bar for everyone else to aspire to.
2. Audio Research.
Again, a brand that has rarely strayed from its roots, has always maintained a point of difference, quality of construction and a devout following. Another rare survivor and I hope they continue.
3. McIntosh.
I'm not a Mac owner, but have seen enough of the internals of Mac gear to respect the history, the designers and their relatively unwavering support in the pursuit of improvements in high fidelity reproduction. Parts are still available for much of their gear and support is excellent.
For notable mentions and companies not necessarily still producing High Fidelity gear:
1. Sony.
Arguably the most innovative and engineering driven electronics company the world will ever see. Their history and dogged determination of their passionate engineers to bring us products that were deemed impossible over many decades is amazing. Their list of achievements is too long to even start.
2. Quad (Acoustical Manufacturing Co. Limited/Quad Electroacoustics)
Producing ESLs, sophisticated amplification, embracing solid state, pushing its boundaries early on and being one of the pioneers of stereo.
3. Matsushita (Panasonic)
For advancing the state of the art with the largest range of superlative and affordable turntables the world has ever seen, through the 1980s when everyone else was moving to digital. They still produce reference-grade new model turntables that are as good or better than anything, regardless of price
4. Rotel.
A small Japanese HiFi only company, family owned that continues to produce very good, affordable, well engineered product and have done for nearly 50 years. The perfect entrance to a quality HiFi journey for music aficionados.
5. Jamo
At one point, the world's largest manufacturer of loudspeakers with the most sophisticated production facility. Produced a huge number of truly excellent loudspeakers, finished and styled with typical Danish attention to detail. Sadly, not sold in great numbers in the US I believe and now a shadow of its former self.
6. Bowers and Wilkins.
Pioneered extremely sophisticated measurements for loudspeakers and advanced the state of the art in loudspeaker design over many decades.
7. JBL.
I don't think there is a more recognizable brand in High Fidelity, known the world over. Yes, Harman had pimped it out and I'm sure Samsung will do the same, but nobody can deny the heritage of the brand and the enormous range of excellent products (along with some horrors) they have produced. Successfully crossed the boundary into professional sound as well as domestic and generally walked a path of improvement and quality, again, over many decades.