The list is of course incomplete, and subjective!

Professional non-profit organisations:

Microwave modelling:
Note: A history and description are given in the section Modelling & Design 

European manufacturers of microwave industrial systems:
Note: The listed companies are well established of which I have good knowledge
Links to several sites (IEC, IEV, JMPEE, Patent offices/searches, the Martin Chaplin water site) are given elsewhere in this site. It may be easiest to go to the Sitemap.