3D Printing
From Hod's Personal Wiki
Tiko
From comments: Hatchbox filament. I only buy Hatchbox now for PLA and ABS. It always works. For nylon I use Taulman
General
Rep Rap (influential open source project)
Blog, filament spools, and a few other items (Oregon)
Steven Devijver writing on building a printer (http://reprapbook.appspot.com/)
Tech Paladin parts (Cupertino)
Inventables "The hardware store for designers" (USA)
Terawatt Industries (parts and printers) (Boulder, CO)
"Taxonomy of Z axis artifacts in extrusion-based 3d printing"