Instruments

Ascent Vario - Portable variometer
Becker Avionic Systems
Blue Sky Avionics - Ball Varios and other instruments
Bohli 
Borgelt Instruments
Cambridge 302 Tips by John DeRosa
Cair Aviation Ltd - a UK producer of variometers, and general instrument supplier
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
Excel file that decodes IGC flight log filenames - by John DeRosa
Filser Electronic GmbH
Finesse Max - French retailer for Schleicher Sailplanes, instruments, software
Garmin
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
Nielsen Kellerman - NK Soaring Instruments
Peschges
RD Aviation - UK 
Sage Variometers 
Soaring Books and Supplies - Bob Wander
SoaringPilot  - Final Glide Calculator for Palm OS Devices - Free
Tasman Instruments - Instruments for Sport Aviation - Australia
Themi - Thermal Centering Device and Logger
Tiger Aviation Services - Online Aviation Superstore
Volkslogger
Westerboer
Wings & Wheels
WinPilot
Winter Instruments
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