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 no cost.

Microphones and audio

Sennheiser MD416-U, Shure BETA 58A, Electro-Voice N/D767a and Shure PG58 dynamic microphones

SM Pro Audio TC01 tube preamp & compressor
dbx 286A and Focusrite VoiceMaster Platinum mic preamps with signal processors
Aphex mod. 612 and dbx 274 expanders-gates

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 Saffire PRO 24
audio & MIDI interface
Presonus Firestation ADAT converter

Farfisa TR70-OS
& Laney AH50 combo amplifier
dB Technology MB80 powered monitor
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 and Alesis Micron polyphonic synthesizers with vocoder
Korg Wavestation EX and Z1 polyphonic synthesizers
Yamaha DX7 (with Grey Matter E! expansion board) and SY35 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
Korg TR 76 music workstation

Korg Prophecy and Monotron monophonic synthesizers

MIDI sound modules

Soundart Chameleon programmable audio DSP engine
Yamaha MU100R XG compatible sound module (with VH-100 & VL-100 expansion boards)
Yamaha TG77 & FB-01 sound modules
Alesis QuadraSynth S4 Plus and QSR sound modules
Korg Wavestation SR, Wavestation A/D, 01R/W, TR-Rackand NS5R sound modules
Roland M-VS1, XV-5050 and P-55 sound modules
Casio VZ-10M sound module
E-mu UltraProteus
sound module
Ensoniq MR-Rack
sound module
Evolution Synthesis EVS-1 digital synthesis sound module
Kurzweil 1000 PX Plus sound module (expanded as 1200 Pro I)
Technics sx-WSA1R acoustic modeling sound module
Voce V3 tonewheel organ synthesizer with MIDI Drawbar controller

Kawai K1m tabletop sound module
Arturia Origin Desktop Virtual Analog DSP tabletop sound module
Zoom RhythmTrak RT-323 rhythm unit

Sound processors

Lexicon Vortex & MPX 1 digital effects processors
Sony DPS-M7, DPS-D7and 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
Yamaha SPX-90 digital effects processor
Zoom 9150 Valve DSP DSP effects processor with valve preamp

Vesta DIG-410
digital delay
Digitech JamMan Solo XT phrase sampler & looper (2 units: 1 )
TC-Helicon VoiceWorks Plus vocal effects processor & harmonizer

MIDI controllers & processors

Studiologic VMK-188 Plus and Edirol PCR-300 MIDI master keyboards & controllers
Roland AX-7 MIDI keytar controller
M-Audio Keystation 32USB mini keyboard (first edition)
Yamaha YDD60 and DD-55 electronic drum machines
Yamaha MFC10 and Rolls/RFX MP1288 MIDIWizard MIDI foot controllers
Behringer BCR2000 and BCN44, Evolution UC-33e, Korg padKontrol, Arturia BeatStep and Kawai MM-16 tabletop MIDI controllers
Casio DH-100 and Yamaha WX11 MIDI wind controllers
Inspired Instruments YRG Gen2 Radius MIDI guitar controller
Roland PK-5 MIDI bass 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

Other stuff

SaeHan SDC63acoustic guitar with built-in pickup
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 music workstation
Roland U-20 poliphonic synthesizer
Roland D-110 sound module
Yamaha MU-80 XG sound module
Lexicon MX200 dual effects processor
Roland TR-707 drum machine
Fostex DCM100 MIDI-controlled audio mixer
Fostex MixTab and 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