Below are listed many of the popular sites.
Balsa Products: http://www.balsapr.com
Bob Selman Designs: http://www.BSDMicroRC.com
Boston Micronauts: http://www.bostonmicronauts.org
Bradley Bros: http://www.parmodels.com
Cox Hobbies: http://www.coxmodels.com
David Lewis: http://www.homefly.com
Dynamic Web Enterprises: http://www.slowfly.com
EFlight: http://www.eflightdesigns.com
Falcon Models: http://www.falconmodels.uk.com
FMA: http://www.fmadirect.com
Gordon's Micro Planes: http://home.comcast.net/~gordon-johnson
Graham Stabler: http://www.indoor.flyer.co.uk
Hobby Lobby: http://www.hobby-lobby.com
Nick Leichty: http://www.microflierradio.com
Jean-Louis Coural: http://www.microplanesolution.com
Jean-Marie Piednoir: http://www.jmp-solutions.com
Jean-Michel Quetin: http://www.jmquetin.com
NEAT Fair: http://www.neatfair.org
Peck-Polymers: http://www.peck-polymers.com
Plantraco: http://www.plantraco.com/hobbies
RC Groups: http://www.rcgroups.com/forums
RC Universe: http://www.rcuniverse.com
Sky Hooks & Rigging: http://www.skyhooks.ca
S. Leicester AeroNutz: http://www.aeronutz.flyer.co.uk
SlowFly: http://www.slowflyworld.de
SlowFlyRC: http://www.smartgroups.com
Tower Hobbies: http://www.towerhobbies.com