Stewart Systems Fabric covering and Waterborne paints
EAA Experimental Aircraft Association
Wag Aero Plans and materials for the 2+2 and other aircraft
SuperCub.org All things related to PA-18 Super Cubs and other Piper long wing tube and fabric aircraft.
Short Wing Piper.org The on-line resource for Short Wing Piper owners and enthusiasts
Supercubproject.com Christian Sturm's Experimental Super Cub Project Includes PA 18 drawings from Piper
j3-cub.com All things J-3 related
Aircraft Spruce Wood and every thing else needed by the Aircraft Home Builder
Wicks Aircraft Great Spruce and lots of other aircraft supplies for aircraft building
metalgeek.com Tube Coping Calculator
WagAero builders group Yahoo builders group supporting all Wag Aero aircraft
Piper Cub builders group Yahoo builders group for Piper Cub, Super Cub and other Cub variants.
McMaster-Carr Hardware, parts, you name it they have it. Not "Aviation" as such but lots of good stuff for homebuilders
Dakotacub.com Super Cub parts and other related goodies
Airframes Alaska More Super Cub and other tail dragger parts and accessories.
Mcfarlane-aviation.com/ Certified aircraft parts