There's no such thing as too many resources for GMs, if you ask me. As such, I direct you towards the Monsters & Magic Compendium that's up on Kickstarter right now from Windmill Slam Games. There's more than a hundred monsters, as well as more than a hundred pieces of magical loot for them to drop.
From the campaign:
Get ready for more than a hundred monsters and a hundred magic items inspired by European legends. With an average of two pages dedicated per monster, every entry contains a ton of background information and extras, including mini-adventures, adventure hooks and items. The stats blocks included are designed for 5e D&D, but this book holds treasures for every RPG enthusiast, no matter which system you prefer, or if you just like to read. Check out our update section for bi-weekly updates and previews!
For GMs: Every monster is designed with care and detail, including introductory tales, descriptions of their biology, behavior and history. We’ve included optional rules, monstrous hooks to inspire you, and mini-dungeons that will provide hours of entertainment. Both the monsters and magic items in this book have been designed to be of use to you no matter which tier your heroes are currently. But there's more...
The Kickstarter is up and over its funding goal, so it's on to stretch goals for the next 24 days.