Your Forever Pieces? What and Why?

ADC XLM phono cartridge - 1968
Teac 4070 reversible tape deck - 1970
Dual 701 semi-automatic direct drive turntable - 1975
Koss Pro 4a headphones - 1976
Marcof PPA-2 battery driven headamp - 1980
Accuphase AC-2 mc cartridge - 1981
Audionics BT-2 preamplifier - 1984
Thiel 3.5 loudspeakers - 1990

Probably a few smaller tape and phono accessories I can't remember as well.

McIntosh MR74. Luxman T110.  Both upgraded by Don Scott about 10 years ago. 

Tandberg 3014a and Nak Dragon.  Bryston 14b3 amp. 

Stax tube-driven headphones (Lambda Signature and 009 phones); Sonus Faber Electa Amator speakers, and Nakamichi cassette deck (RX-505). All owned (except Stax 009s) since the early 90's.

Judging on how long I've owned them:  My Conrad Johnson Premier 12 tube monoblock amps.
I bought them in the late 90's as I remember and they've been my main amplifiers since.  Such a hard to find combo of tube lushness yet focused, punchy and well controlled from top to bottom on whatever speakers I put on them.