FX units
Only (19") units for "professional use" are stated.  By no means is it complete. There is too much out there, I've only named what I've seen used by pro's. This list also contains hybrid systems (preamps + fx), but again not everything is stated. And I won't try to.

3630 Compressor   2 channels, 1U
Nancompressor   1/2 19", stereo, 1U
NanoVerb   1/2 19", reverb + fx, 1U, midi
MIDIverb 4   reverb + fx, 1U, midi
Q20   fx, 1U, midi
Quadraverb   reverb, 1U, midi

Aural Exciter C2   enhancer/exciter, 1U

Autocom PRO MDX-1400   2 channel compressor, 1U
Composer PRO MDX-2200   2 channel compressor/limiter, 1U
T-1952 Tube-Composer   as MDX2200 but tube driven, 2U
Multicom PRO MDX-4400   4 channel compressor/limiter, 1U
Intelligate XR-2000    2 channel gate, 1U
Multigate PRO XR-4400    4 channel gate, 1U
Multiband Denoiser SNR-2000   2 channel denoiser/noise gate, 1U
Ultrafex Pro EX-3200   stereo enhancer/exciter/surround sound/noise reduction, 1U
T-1954 Tube Ultrafex    tube version of the EX-3200, 2U

862   stereo enhancer/exciter + noise reduction, 1U
46..   stereo enhancer/exciter
36..   stereo enhancer/exciter

NS-2   Custom 19" Noise gate, 1U  *?
NS-50   1/2 19", noise gate, 1U  *?

Digital Delay   1U

Custom Shop

Custom Audio Electronics:
Super Tremelo   1/2 19", tremelo, 1U
Custom Shop

266XLV   2 channel compressor, 1U
166-XL   as 266
160-AD   as 266 but only one channel, 1U
1066A    2 channel compressor/limiter/gate, 1U
1046   as 1066A but 4 channel, 1U
120XP   subharmonic synthesizer, 1U

GSP-21 (Pro, Legend)   preamp (solid state) + stereo fx, 1U, midi   *
Valve FX   tube preamp + stereo fx, 1U, midi  *
GSP2101 (Artist)   tube preamp + stereo fx, 2U, midi  *
VGS-2112   tube preamp + stereo fx, 2U, midi  *
VGS-2120   tube preamp + stereo fx, 2U, midi
Quad-4   4 in/out, fx, 1U, midi
DSP-16   fx, 1U, midi  *
DSP-256 XL   fx, 1U, midi  *
TSR-24   fx, 1U, midi  *
DHP-55   pitchshifter + fx, 1U, midi  *
Super Harmony Machine  pitchshifter, 1U, midi  *
IPS-33B   pitchshifter, 1U, midi  *

DL-241   dual auto compressor, 1U
MX-30   gated compressor/limiter, 2 channel, 1U
DS-201   dual noise gate, 1U
DS-404   quad noise gate, 1U
MX-40    quad noise gate, 1U

DCR-15R Crybaby Rack   19" wah, several options, 4 connections, 1U

Custom Shop

DSP-7000   fx, 2U, midi
H-3000 D/SE   fx, 2U, midi
H-3000 D/SX   guitar version of SE, 2U, midi   *
Eclipse   fx, 1U, midi
DSP-4000B   fx, 2U, midi
GTR-4000   fx, 2U, midi
DSP-4500   fx, 2U, midi
ORVILLE   4 in/out, fx, 2U, midi
H3000B+ and H3000B/LT
H910 Harmonizer    *
H949 Harmonizer    *
HM80 Harmonizer   *
H969 Harmonizer   *
SP2016 Effects Processor    *
FL201 Instant Flanger   *
PS101 Instant Phaser   *
2826 and 2830 Omnipressor   *
JJ193 and CD254 Delay Lines   *

PL...   power distribution, 1U
Isopatch   groundloop hum solution, small

Klark Teknik:
DN 3600   2x30 band graphic EQ, progr, 2U, midi
DN 6000   2x31 band graphic EQ, progr, 2U, midi

DTR-1   rack tuner, 1U

MPX-G2   stereo fx + solid state preamp, 1U, midi
MPX-500   fx, 1U, midi
MPX-1   fx, 1U, midi
PCM-81   fx, 1U, midi
PCM-91   fx, 1U, midi
PCM-60   fx, 1U, midi  *
PCM-70   fx, 1U, midi  *
PCM-80   fx, 1U, midi  *
PCM-300   fx, 1U, midi  *
PCM-480   fx, 1U, midi  *
PCM-41   fx, 1U, midi  *
PCM-47   fx, 1U, midi  *

R450 Strobe Tuner   3U 

GM-1000   preamp (solid state)+ fx, 1U, midi
Echoplex   delay/looper, 1U, (midi?)

PGE-2   progr 14 band eq, 1U, midi  *
Smart gate   1/2 19", mon noise gate  *

Intellifex   fx, 1U, midi
Chameleon   preamp + fx, 1U, midi
Voodoo Valve   preamp + fx, 1U, midi
Phrophesy   preamp + fx, 2U, midi
MultiValve   fx, 1U, midi
Intellipitch   pitchshifter + fx, 1U, midi
Hush Super C   noise reduction, 1U
Replifex   fx, 1U, midi
Pro Q   progr EQ, 1U, midi  *
300 G   guitar compressor, 1U  *
Guitar Silencer   stereo noise gate, 1U  *
Hush IIBX/CX   (CX=stereo) noise gate, 1U  *
Pro Hush   stereo noise gate, 1U  *
DVC   Dynamic Volume Controller, midi, 1U  *

SRV-3030  fx, 1U, midi
SRV-330   reverb, 1U, midi
SDE-330   delay, 1U, midi
SDX-330   fx, 1U, midi
Roland GP-100   preamp + fx, 1U, midi

Powerbrite   power distribution, 1U

Tremelo Reverb   2U

DSP V-77   fx, 1U, midi
DPS V-55M   fx, 4 in/out, 2U, midi

Stereo Vizalizer JACK   enhancer/exciter, 1U
Stereo Vizalizer MK-II   as JACK + compressor, 1U

TC Electronic:
M3000   fx, 1U, midi
M2000   fx, 1U, midi
Fireworx   fx, 1U, midi
G-Force   fx, 1U, midi
G-Major   fx, 1U, midi
TC 2290   fx, audio/function switching, 2U, midi  *
1210 Spatial Expander   chorus/flanger, 1U  *
1140 parametric EQ and preamplifier   1U   *

Valvulator 1   small, tube driven buffer line driver (to avoid signalloss)

SPX-990   fx, 1U, midi
SPX-90   fx, 1U, midi  *
SPX-1000   fx, 1U, midi  *
ProR3   fx, 2U, midi
D-1500  digital delay, 1U  *