As an instrumentation engineer, I used to spend a lot of time searching on the web for such web sites.
I was lucky to find some websites, or to explore websites referred by friends.
else, I shall have to go to instruments companies websites, where they try to lead you to use their products.
http://www.automation.com/ is one of these informative sites that I was lucky to find.
Actually, it's kind of a comprehensive instrumentation site.
They have everything from a web store for instrumentation products.
an index of suppliers, and products where you can search both.
Tons of articles, tutorials, and best of all "Instrumentation stories" where you can check solutions made in different places.
And above all, a "Resources" link.
I'd say it's a relatively rich resource.
Check it out and enjoy.
Book of the Day
I will try to stick to the subject of the post when I pick the book of the day.
This is a book that will teach you the basics of instrumentation, and will add more of course.
Enjoy it :