What's the best and/or favorite piece of equipment you've owned? And do you still own it?

Lot's to choose from but probably my Nakamichi Dragon. I was a cassette deck-aholic! Next would be my 70lb Thorens TD125 Black Forest Edition with SME Series 3 tonearm and Shure cartridge. Currently I love my KEF R series speakers and SVS SB 3000! I'm now an HT junkie...

Oops right in addition to the Ohm Walsh since 1982 there is my Linn Axis since 1986.

My Apogee Duetta Signatures. Purchased in 1991. Still the centerpiece of my system.

For me it’s my Shindo Monbrison preamp.  I had discounted the importance of the preamp in my system before I got that one about 5 years ago, even though I had gone through some good ones.  
The Shindo just made everything sound better, full and rich and layered and textured and natural, with lots of detail, no matter what other components or music I throw at it (and I’ve changed a lot of components during the last 5 years). I doubt I’ll ever part with it, unless somehow I can afford to go further up the Shindo preamp chain, which would be quite expensive.  
And no, I’m not a believer that it has to be all Shindo or no Shindo.  It’s my only Shindo component (outside of some cabling), and I think at least at the preamp level it’s astoundingly good by itself, at least to my ears.  

The KLH Nine full-range electrostats I bought in 1991 from HiFi Classics in Far Rockaway, NY. $500 - and a major bargain! Still have them in occasional use along with the pair of Futterman H3aa OTL amps.