A very helpful resource which I had vaguely been aware of for a while but which I have only recently starting using more regularly is the Regesta Imperii OPAC Literature Database for the Middle Ages (RI-OPAC), available in English as well as German.
The database lists over 2.5 million academic books and articles on medieval topics, searchable by author, title, and thematic tags. Since it is limited to medieval research, even a search for a single word (e.g. ‘counsel’, ‘gestures’, ‘kingship’) tends to be much more fruitful than searching the entirety of a research library catalogue. While not exhaustive, the database is regularly updated and is therefore an excellent tool for investigating what research has already been done on any particular topic.
Scrawling Spires 