List of Research Institutes (excluding universities)!
After some further search I found exactly what I was looking for:


  https://en.wikipedia.org/wiki/Category:Research_institutes


or by country:


  https://en.wikipedia.org/wiki/Category:Research_institutes_by_country


This comprehensive list includes the majority of all existing research institutes and definitely all notable one's. However, there is of course no ranking provided (which is not a problem for me but may be for other people that visit this question).