House Greydragon - Lots of how-to information on tents, furniture and more. Pictures of two extant tents in museums.
Steven Bloch's Tent page - More info on tents, especially good collection of period paintings
Max and Mikel's No-Bake Pavilion - A how-to page for a style of round pavilion. Some useful ideas here, particularly if you don't have a heavy duty sewing machine.
Medieval Pavilion Resources - The mother of all Pavilion link pages. Sadly, a great many of the links are now broken, but it's still worth checking out.
History of Tents - A survey of tents in period art. Little of the art is actually available on-line, but descriptions are given as well as books/museums where the original piece can be found.
Bibliothèque Nationale de France - Several Manuscripts on-line including Froissart's Chronicles
Web Gallery of Art - Lots of art on-line, a tiny bit of it has tents and is pre-1600.
Dragonwing - No longer selling tents, but still a wealth of good tent related info.
German History Museum - A photo diary of the restoration of a turkish tent from 1683.
House Greydragon - Not just tents, but quite a few articles on reproductions of medieval and renaissance furniture as well.
Blood and Sawdust - A period woodworkers site. Many articles, lovely work.
Peter Follansbee's blog - Peter speciallizes in 17th century American furniture, but does amazing work and has a wealth of information on early woodworking.
Logan Cabinetshop - Like Follansbee, he concetrates on 17th century American furniture, but tons of good info for handtools and early woodworking.
Robin Wood - Robin is a traditional turner. As such, there is less here about furniture, but again, a great read for the early woodworker.
St. Thomas Guild - A European re-enactor group focused on a woodworking guild. Lots of nice stuff.
Sources for Materials:
Canwil - I've recently begun switching to Canwil's fabric. They are slightly more expensive than ITEX (below) but the fabric is really nice..
ITEX - or (800)-525-7058. If you are building a couple of tents, Dan Love at ITEX can take care of you. 100 yard rolls (or larger). For smaller quantities contact me.
Jason Townsend and Son - Best place I have found so far for cotton webbing for ties, stake loops etc.
R&W Rope Warehouse - My current supplier for rope. Also, they carry sewing palms, sailmaker's needles, and other handy tools.
Rawganique - Mostly organic apparel, but also have pretty nice eastern european hemp rope. The supplier/exporter went out of business for a time, but appears to be back up and running.
Other Tent makers:
Panther Primitives - Probably the largest "period" tent makers in the world.
Tentsmiths - Website looks nice. I haven't personally seen any of their tents.