Everything listed at
http://www.bestrc.com is distributed by the Great Planes/Hobbico/Tower conglomerate
Horizon Hobby
http://www.horizonhobby.com is the distributor for JR, Saito, Hangar 9, Seagull, and MANY others.
These two appear to be the biggest players.
Global
http://www.globalhobby.com distributes quite a few brands and their retail arm is
http://www.hobbypeople.net
Ace
http://www.acehobby.com is the distributor for Ace & Thunder Tiger.
http://www.thundertiger4u.com carries a good selection of these items.
The other places listed (Advantage, MyAtomic, Ultimate, etc) buy from the big distributors. Sometimes they have better pricing than the "big guys" and sometimes they do not. One advantage to some of these sellers is that you can place one order and get things from nearly all of the distributors.