Canvas Falcon Engineering - World War One airplane preservation.
Rosebud's Aviation Archive -  large collection of aircraft photos (allow some time for home page list to open.)
The Aerodrome - WWI aviation site with large data base and registered discussion forum.
Please Note:  I have listed some links already used in various places on my site.  If you have a propeller related link that you would like me to include, please let me know.
Sensenich Propeller - manufacturing wooden propellers since 1932, they are still in business.  They have lists of dates relating to serial numbers, and most model numbers can be looked up by searching under aircraft types.
WW1 Aviation Links - just what the title says, a collection of resources on the internet, (some of which are already listed here.)
Vintage Aviation - "Our mission is to serve the community of WW1 aviation enthusiasts."
Replicraft - WW1 modelers site with a large set of WW1 aircraft plans and color documentation options.
Chad Wille - St. Croix Propellers.  Designer and manufacturer of custom wood propellers for homebuilt and antique aircraft.  Also does propeller restoration.  Chad has kindly provided me with some of the technical information about propellers used on this site.
Aircraft Engine Historical Society - engine development, manufacture, and use.
Over the Front - Journal and web site of the League of WW1 Aviation Historians
Fokker-Team-Schorndorf -  information primarily on early German aircraft.  Reproduction Axial propellers and drawings.
Wings of History Prop Shop  - Guy Watson is continuing propeller construction originally carried out by well known propeller designer and maker,  Ole Fahlin.
Aeroclocks -  Bob Gardner's British site - has some WW1 and other propellers for sale. 
Holcomb's Aerodrome - general interest with abundant links to aviaiton sites
Propeller Interest:
Modern Wooden Propellers - a new site focusing on post 1920 era wooden propellers, developed in conjunction with this site.
SpitfireSpares - British company manufacturing WW1 propeller replicas
Constant Speed (Variable Pitch) Wooden Propellers - a collection of variable pitch propellers, and information about them.
Decals  - can be custom made by Nostagic Reflections
New Site: Polish propellers - a site focusing on propellers relating to polish manufacturers and aircraft
These sites were previously active but now return loading errors:
Updated July, 2021