In late 1982, Gary Gygax published this second volume of the Monster Manual. While the first monster manual concentrated on the usual orthodox creatures which have become AD&D canon, the second volume extended this, especially encorporating many other-planar beings, demons, devils, real-world wild animals, dinosaurs, and other fantastic creations. All in alphabetical order for ease of finding.
To give a sample - here are some examples of the monsters herein.
REAL WORLD ANIMALS - falcon / hawk, eagle, cat, cheetah, "minimals" - great resource
DEVILS - Glasya, Belial, and the popular bearded devil.
DEMONS - Graz-zt, Baphomet
DINOSAURS - mainly minor dinosaurs not covered in MM1, including Kentrosaurus (small stegosaurus) - not really essential for most campaigns
OTHER FANTASTIC CREATIONS - bookworm, luck eater, cat lord, mud-man