I'm going to recommend Volo's Guide to Monsters. There is expansion on Beholders, Demons, Dinosaurs, Giants, Gnolls, Hobgoblins, Kobolds, Mind Flayers, Orcs, and Yaun-Ti. They also added an abjurer (CR 9), archdruid (CR 12), archer (CR 3), blackguard (CR 8), champion (CR 9), conjurer (CR 6)...