In an effort to create a research starting point for members looking to buy a tri bike, in August of 2008 I asked LA Tri Club members to tell me their tri-bike make and model. Here is a list of triathlon bike makers, from the mass made to the custom. Of 63 respondents, the number in parenthesis indicate the number of tri club members who ride that brand. 

Aegis

Argon18

BH

Blue

Calfee (1)

Cannondale (1)

Cervelo (20)

Colnago

Elite (2)

Felt (5)

Fondriest

Fuji

Giant

Griffen (1)

Guru (1)

Isaac

Jamis (1)

Javelin

Kestrel (4)

Kuota (7)

Leader - frames only

Litespeed

Look

Lynskey (1)

Orbea (2)

Parkpre (1)

Planet X (1)

Pinarello

Predator

Quintana Roo (4)

Ridley

Roark

Scott (1)

Seven (1)

Softride - no longer making bikes (1)

Specialized (1)

Teschner

Titanflex (2)

Trek (4)

Valdora

Wilier Triestina

XLAB

For those interested, here is how the list breaks down by model:

Maker Model Count

Calfee Luna : 1

Cannondale Ironman : 1

Cervelo P2C : 4

Cervelo P2SL : 2

Cervelo P3 : 5

Cervelo Soloist : 3

Cervelo P3C : 2

Cervelo P3SL : 1

Cervelo SLC-SL : 1

Cervelo Dual : 2

Elite Time Trial : 2

Felt S22 : 2

Felt S32 : 1

Felt (unspecified) : 1

Griffen : 1

Guru Crono : 1

Jamis Comet : 1

Kestrel Airfoil Pro : 2

Kestrel Talon : 1

Kestrel Talon SL : 1

KHS : 1 (this is a road bike and therefore not included in the above data)

Kuota K-Factor : 4

Kuota Kueen K : 2

Kuota Kalibur : 1

Lynskey Level 4 : 1

Orbea Aletta : 1

Orbea Diva : 1

Parkpre Image TT : 1

Planet X Stealth : 1

Quintana Roo Seduza : 3

Quintana Roo Picante 650 : 1

Scattante CFR (Performance Bike house brand, technically a road bike) : 1

Scott TT : 1

Seven Custom : 1

Softride Rocketwing : 1

Specialized Transition : 1

Titanflex Terminator : 1

Titanflex Veteran : 1

Trek Project One : 1

Trek Madone 5.2 : 1

Trek Equinox7 : 1

Trek Equinox 9.9 TTX : 1