This is my personal list of manufacturers, which I’ve dealt with during my research life. Sorry I don’t have time to kill dead links or organize it nicely... still, it works for me and my students, could be useful for you as well :).
It is not always possible to classify a company, especially large one, into just one category. In that case, its name may appear in several parts of the list or in the one that is most relevant to me.
Companies and their sites sometimes change faster than I can follow. If you encounter a broken or misleading link in my list,
please consider it as indication of company's attitude towards its customers.