The greatest classic of the genre: Ivanhoe. Written in the 1800s, it feel its age, but to some (i.e. me and hopefully others) it just add to the charm. So much adventure on a very romanticized medieval background.
The Arthurian cycles: if you are not looking for historical accuracy are are fine with a little magic sprinkled around. Many authors retold the legends, there are the old french novels (by Chrétien de Troyes - a bit stiff at times and formulaic) or the more modern ones. My personal favorite is the cycle by Mary Stewart, but “The Once and Future King”* is also really good.
An adventurous take on the fall of the Roman Empir: The last Legion by V M Manfredi*.
A view on the life of common people during the middle ages, developed around a compelling plot: the quadrilogy by Valeria Montaldi.
The ones you can’t overlook: Pillar of the Earth by Ken Follett and Cathedral of the Sea by Idelfonso Flacones. Flavor-wise I felt they were very similar, a broad cast of characters with strong emotions moving on the backdrop of the gothic revolution. Particularly good if you like architecture.