Instruments
Ambry - Batteries and other spare parts for Compaq Pocket PC's
Ascent Vario - Portable variometer
Becker Avionic Systems
Blue Sky Avionics - Ball Varios and other instruments
Bohli 
Borgelt Instruments
Cambridge Aero Instruments
Cambridge 302 Tips by John DeRosa
Cair Aviation Ltd - a UK producer of variometers, and general instrument supplier
CEGlide - Affordable final glide software for soaring pilots
Composite Technologies - Gauteng, South Africa
Crabb Computing - UK retailer of soaring software and instruments
Craggy Aero
Cumulus Soaring, Inc. - Paul Remde - Instruments, software and accessories. 
Dittel, Walter - Radios
Eastern Sailplane
Electronic Thermal Detection - Martin Gregorie - Ground based solution for detecting thermals
Electronic Variometer - Marko Rocznik - Design of an electronic vario
Entec Technical Services - Horseheads, NY, USA, Dealer for Komet and Volkslogger
EW Avionics
Excel file that decodes IGC flight log filenames - by John DeRosa
Filser Electronic GmbH
Finesse Max - French retailer for Schleicher Sailplanes, instruments, software
Garmin
Garrecht - Volkslogger
GPS Data Logger
Holtronic GmbH - Cenfis
How to Build Instruments for Hang Gliders - Fred Vachss - Interesting
ILEC GmbH
Knauff & Grove Soaring Supplies
LX Navigation
LX avionics Ltd - UK distributor for Filser and LX products, Oxfordshire, England
Mallettek Mini Vario
Ian McKee Aviation - Instruments, radios & maker of microphones and wingstands - NSW, Australia 
Microair Electronics Pty. Ltd.
Mountain High Equipment & Supply Co. - Aircraft Oxygen Equipment
New Technologies - Easy Matchbox Variometer - Italy
Nielsen Kellerman - NK Soaring Instruments
NMEA Recorder - Nick Bonničre
Peschges
PZL - WARSZAWA II S.A., Wytwórnia Sprzętu Komunikacyjnego (WSA) - Variometers, Airspeed Indicators, Altimeters - Poland
RD Aviation - UK - Online store is here
Sage Variometers
SDI Variometer - Varios, flight recorders, navigation
Soaring Books and Supplies - Bob Wander
SoaringPilot - Final Glide Calculator for Palm OS Devices - Free
Solaire Canada - Canadian Dealer for LS (Rolladen-Schneider) Sailplanes, instruments, trailers, etc.
Tasman Instruments - Instruments for Sport Aviation - Australia
Themi - Thermal Centering Device and Logger
Tiger Aviation Services - Online Aviation Superstore
Volkslogger
vPos - Virtual Position software and hardware for real-time tracking of gliders and viewing in 3D.
Westerboer
Wings & Wheels
WinPilot
Winter Instruments
Wytwórnia Sprzętu Komunikacyjnego (WSA), "PZL - WARSZAWA II" S.A.  - Variometers, Airspeed Indicators, Altimeters - Poland
XCOM Avionics - Aircraft radios and intercoms - Australia - Available from www.cumulus-soaring.com
Zander
Zaon Flight Systems, Inc. - Portable Aircraft Collision Avoidance Systems, Frisco, Texas, USA