Much of the quality and variety of what I build depends on the quality and variety of parts and materials that I can source. To this end, I collect and semi-religiously thumb through catalogs. (Yes, most of these places also have Web sites, but sometimes catalogs are just easier, or at least more fun.) Whether for selection, esoterica or service, here are my six favorite vendors for all my project needs. Got a favorite of your own? Tell us about it in the comments.