[shamelessplug] I run a factory tours meetup group in the Bay Area. We've been to machine shops, injection molders, foundries (metal not semiconductor), among others: http://www.meetup.com/Bay-Area-Factory-Tours/

Another one just started in Boston: http://www.meetup.com/New-England-Factory-Tours-Meetup/

Attendance is free--just sign up to the tours you're interested in.

Let me know if you want to spin one up in your area/if you have an idea for a tour. [/shamelessplug]