Dedicated 19" (tube) Preamps
Only 19" preamps that are used 99% of the time as a preamp only, are stated here. There are some hybrid systems (preamp + fx) too, but they can be found in the FX section.

ADA:
MP-1 (Classic)  progr, midi, 1U  *
MP-2   progr, midi, 1U  *

Art:
SGX LT   1U, solid state  *
SGX Nitro   1U, solid state, progr, midi  *
SGX 2000(SE)   2U, solid state, progr, midi  *
SGE   1U, solid state, progr, midi  *
SGE Mach II   1U, solid state, progr, midi  *

BBE:
381   1U, (solid state?)  *

Bogner:
Fish    4 ch, 2U   *  
Triple Giant    3 ch, 2U  *  

Brunetti:
Centouno   3 ch, (midi), 1U
Mille   4 ch, (midi), 2U

Carvin:
Quad X-Amp   4 ch, midi, 2U  *
SX-15   2ch, 1U, midi, solid state

Climax:
S3   3 ch, 2U  *

Crate:
TDP   2 ch, 1U, solid state  *
XLP   2 ch, 1U, solid state  *

Custom Audio Electronics:
(SE) 3+   3 ch, 2U  

Demeter:
TGA

DigiTech:
Twin Tube   progr, midi, 1U  *

Egnater:
IE4   4 ch, 2U, midi   *  
Modular Guitar Tube Preamp   4 ch, 2U  

Engl:
520   3 ch, 1U  *  
530   3 ch, 1U  
580   progr, midi, 2 U  
620   2 ch, 1U  *  

Ernst:
Rover   4 ch, midi, 2U  
Unknown   3 ch, 2U  *  

Exef:
4 Tune   4 ch, 2U

Groove Tubes:
Trio Preamp (Deluxe)   3 ch, (midi), 2U  
Studio Preamp   1ch

Hafler:
Triple Giant   3 ch, 2U  *  
T2   2 ch, 1U  *
T3   3 ch, 1U  *
Hellrazor   2 ch, 1U  *

Hughes & Kettner:

Access   progr, midi, 2U  *
Tubeman Plus   4 ch, 1U, (midi)  *?
Attax   2ch, 1U  *?

Jackson:
JX-3   1U   (solid state?)  *

Kasha:
Rockmod II   1U, 3 ch  *
Rockmod III   1U, midi, 3 voices  *

Kitty Hawk:
Quattro Preamp   1U  *
Testarossa  *
Stage 2003   1U, 3 ch *

Kolbe:
GP-1    2 ch, 1U

Lag:
TL1 Spitfire    2 ch, 1U, uses 2 12AT tubes  *

Lexicon:
Signature 284   1 ch, recording amp, 2U

Line 6:

Pod-Pro   progr, midi, 2U, solid state

London Power:
Sustainor   2 ch, 2U

Marshall:

JMP-1   prog, midi, 1U
MR-9004   2 ch, 1U, solid state  *
MR-9001   3 ch, 1U  *

Mesa/Boogie:
Triaxis   prog, midi, 1U  
Quad   4 ch, 3U  *  
Studio   3 ch, 2U  *  
Formula   3 ch, 1U  
V-Twin Rack  2 ch, 1U  *
Rectifier   3ch, 2 U  

Peavey:
Rockmaster   3 ch, 1U  *?
TG Rexx    *

Rath:
The Preamp   solid state  *

Rockman:
Sustainor   1/2 19", solid state  *
Distortion Generator   1/2 19", solid state  *
XPR a   1/2 19", solid state  *

Rocktron:
Egnater IE4   4 ch, 2U, midi  
Piranha   prog, midi, 1U
Gainiac   1U, (solid state?)
Maxe   1U, (solid state?)  *
Pro G.A.P. (Ultra)   1U, (solid state?)  *
Sidewinder   3ch, 1U  *

Soho:
QTR-1    4ch, 1U - based on Kitty Hawk Quattro  *

Steavens:
The Counterpoint Preamp

Soldano:
X-99 Caswell   prog, midi, 2U
X-88   3 ch, 2U
SP-77   2 ch, 2U  *?

TC Electronics:
TC1140  Parametric EQ and preampflifier   *

Tech 21:
SansAmp PSA-1   progr, midi, 1U, solid state

Trace Elliot:
TVT9   2 ch, 2U  *

Tube Works:
9002 Real Tube 2   2 ch, 1U
Real Tube II   2 ch  *
RT-992   2ch  *

VHT:
Valvulator GP-3   3 ch, 2U

Voodoo Lab:
Guitar Preamp   3ch, 1U

Yamaha:
DG-1000   prog, midi, 2U, solid state