I think the list of suppliers needs some adding on to.
Large suppliers for all kinds of raw materials, tools, electrical components, all kinds of shit really.
http://www.mcmaster.com
http://www.grainger.com
http://www1.mscdirect.com/cgi/nnsrhm
A few more geared towards machinery/automation
http://www.automationdirect.com -cheap PLCs among other things
http://www.sdp-si.com -stock drive products, gears, shafts, motors, couplings, pulleys, belts, that kind of stuff
http://www.keyence.com/usa.php -fancy pants sensors
and one of the greatest product lines ever created
http://www.8020.net
'The industrial erector set.' At my job we use 80/20 stuff to build a lot of our machinery.