This list is not intended as any kind of "endorsement" about the listed items!
Most of this stuff has been bought used or acquired at zero cost.
Microphones and audio
Sennheiser MD416-U, Shure BETA 58A, Electro-Voice N/D767a & Shure PG58 dynamic microphones
Aston Spirit studio condenser microphone
SM Pro Audio TC01 & TC02 tube preamps with optical compressor
dbx 286A & Focusrite VoiceMaster Platinum mic preamps with signal processors
Radial Engineering Tonebone Loopbone master fx loop pedalboard controller & booster
Aphex mod. 612 & dbx 274 expanders-gates
Aphex mod. 104 Type C2 aural exciter
Rolls/RFX RP93S Patchwork MIDI-controlled audio switcher
Kawai MX-8SR 16-inputs analog stereo rack mixer
Montarbo PROMIX 573 12-inputs analog stereo mixer
TAPCO (by Mackie) 6306 6-inputs analog stereo mixer
Fostex VM200 & Event EZbus digital mixers
Focusrite Scarlett 18i20 3rd generation & Saffire PRO 24 audio & MIDI interfaces
Presonus Firestation ADAT converter
Behringer SRC2496 A/D-D/A & sample rate converter
Numark M101USB DJ mixer with USB audio interface
Farfisa TR70-OS & Laney AH50 combo amplifier
dB Technology MB80 powered monitor
Alesis Elevate 5 MKII paired powered studio monitors
Zoom 7010 Fire & Roland Mobile Cube mini-amplifiers with effects
Keyboards
Farfisa VIP-370 analog electronic organ
Rhodes Fifty Four electric piano
ELEX K3 analog electronic piano
Novation UltraNova & Alesis Micron polyphonic synthesizers with vocoder
Korg Wavestation EX & Z1 polyphonic synthesizers
Yamaha DX7 (with Grey Matter E! expansion board) and Reface DX polyphonic synthesizers
Radikal Technologies Accelerator polyphonic synthesizer (with one DSP expansion)
Ensoniq VFX-SD polyphonic synthesizer
Kawai K4 polyphonic synthesizer
M-Audio Venom polyphonic synthesizer
Roland D-50 polyphonic synthesizer
Waldorf Blofeld KB (black) polyphonic synthesizer
Korg 707 strap-on polyphonic synthesizer
GEM Equinox 61 music workstation
Kawai K5000W "Enhanced" music workstation
Studiologic Numa Compact 2x & Yamaha YC61 stage keyboards
Korg Prophecy & Monotron monophonic synthesizers
MIDI sound modules
Soundart Chameleon & Zynthian V4 programmable audio/MIDI DSP engines
Yamaha MU100R XG compatible sound module (with VH-100 & VL-100 expansion boards)
Yamaha TG77 sound module
Korg Wavestation SR, Wavestation A/D, 01R/W, & TR-Rack sound modules
Roland M-VS1 & P-55 sound modules
Alesis QuadraSynth S4 Plus sound module
Casio VZ-10M sound module
E-mu UltraProteus sound module
Ensoniq MR-Rack sound module
Evolution Synthesis EVS-1 digital synthesis sound module
Technics sx-WSA1R acoustic modeling sound module
Voce V3 tonewheel organ synthesizer with MIDI Drawbar controller
Kawai XD-5 percussion synthesizer
Casio FZ-10M sampler
Kawai K1m tabletop sound module
Boss DR-5 & Zoom RhythmTrak RT-323 rhythm units
Artiphon Orba & Zoom ARQ Aero RhythmTrak AR-96 rhythm unit, sequencer, MIDI controller, etc.
Sound processors
Lexicon Vortex & MPX 1 digital effects processors
Sony DPS-M7, DPS-D7 & DPS-F7 digital effects processors
Alesis Akira & QuadraVerb Plus digital effects processors
Boss SE-70 digital effects processor
Digitech TSR-24S digital effects processor
Ensoniq DP/2 digital effects processor
Korg A1 digital effects processor
Roland RSP-550 digital effects processor
Viscount ER-256 digital effects processor
Yamaha SPX-90 digital effects processor
Zoom 9010 & 9150 Valve DSP digital effects processors
HeadRush MX5 digital effects pedalboard
Chaser EP-100 analog delay
Vesta DIG-410 digital delay
Digitech JamMan Solo XT phrase sampler & looper [2 units]
TC-Helicon VoiceWorks Plus vocal effects processor & harmonizer
Red Sound Systems Federation BPM FX-Pro effects processor & MIDI syncronizer
Korg Kaoss Pad 3 effects processor, looper, synth etc.
Zoom MS-70CDR multieffects pedal
MIDI controllers & processors
Studiologic VMK-188 Plus & Edirol PCR-300 MIDI master keyboards & controllers
Roland AX-7 MIDI keytar controller
M-Audio Keystation 32 (first edition) USB mini keyboard
Yamaha YDD60 electronic drum machine
Yamaha MFC10, M-Vave Chocolate & Rolls/RFX MP1288 MIDIWizard MIDI foot controllers
Behringer BCR2000 & BCN44, Evolution UC-33e, Korg padKontrol, Arturia BeatStep, Kawai MM-16 & Vestax PAD-One tabletop MIDI controllers
Casio DH-100 & Yamaha WX11 MIDI wind controllers
Inspired Instruments YRG Gen2 Radius MIDI guitar controller
Roland PK-5 MIDI bass pedalboard
M-Vave Chocolate wireless MIDI switch pedalboard
MOTU MIDI Timepiece AV-USB rack MIDI interface
Miditemp MP-44 MIDI player & matrix
JL Cooper Nexus Plus MIDI patchbay
Waldorf MIDIBAY MB-15 MIDI patchbay
Anatek SMP-16 MIDI and audio patchbay
Yamaha MEP4 MIDI event processor
MIDI Solutions Event Processor Plus pocket MIDI event processor
M-Audio Mid Air MIDI wireless system & USB interface
HobbyTronics USB-MIDI-CONV2 & Kenton MIDI USB Host MkII MIDI-USB host interfaces
Other stuff
SaeHan SDC63 acoustic guitar with built-in pickup
Ibanez Silver Cadet "Z" electric guitar
DG De Gregorio Yaquì Makassar cajón
LP Latin Percussion Cyclops LP150 hand tambourine
Tycoon Percussion Twin Shakers
Tycoon Percussion TWM-70 hand cowbell
Hohner Blues Harp diatonic harmonica (tuned in G)
Hering Rollinha double diatonic harmonica (tuned in D and G)
The huge computer hardware and software (Atari ST, Mac, PC) is voluntarily excluded, as well as the accessories (memory and sound cards, stands, bags & cases, lots of cables...).
Not available anymore
Korg MS-20 analog monophonic synthesizer
Yamaha EX5 & Korg TR 76 music workstations
Roland U-20 & Yamaha SY-35 poliphonic synthesizers
Roland D-110 & XV-5050, Alesis QSR, Kurzweil 1000 PX Plus (expanded as 1200 Pro I), Yamaha FB-01 & Korg NS5R sound modules
Yamaha MU-80 XG sound module
Arturia Origin Desktop Virtual Analog DSP tabletop sound module
Lexicon MX200 dual effects processor
Roland TR-707 & Yamaha DD-55 drum machines
Fostex DCM100 MIDI-controlled audio mixer
Fostex MixTab
& Novation Nocturn tabletop MIDI controllers
Tascam Ministudio Porta One 4-tracks cassette recorder
Anatek Pocket Record MIDI recorder
Yamaha BC1 breath controller
M-Audio MidAir 25 wireless MIDI master keyboard & controller
JL Cooper MSB Plus rev.2 MIDI patchbay
Mad Catz Mustang Pro MIDI guitar controller