Reddit reviews A Wizard's Bestiary

Of the ones mentioned I have only read the D&D stuff and Barlowe's Guide to Fantasy, both of which are good times but of course are concerned with creatures that have already been developed by various authors, which you might not be as excited about if you're looking for original inspiration. The D&D books are the better for that.

Another couple of books: A Wizard's Bestiary, which is similar to the Carol Rose books in that it is chock full of short entries on a wide range of critters. Potential downside: it is very New Agey at times. Interesting twist: the author has a thing for trying to find real-world explanations for various monsters, which is alternately interesting and ridiculous. Also, he once bred a one-horned goat and exhibited it as a unicorn.

Brewer's Dictionary of Phrase and Fable: Which is more of a general reference for folklore, tradition, sayings and other weird things than a bestiary but is basically an idea-generator. I just flipped through a copy and learned of the gyrtrash, a spectral dog or donkey that waylays travellers on lonely English roads.

I linked to one of the modern editions, which are fine books, but I also have a lot of affection for the older ones, before the mid-Nineties or so. They had this very charming Victorian sensibility that added flavour to many of the descriptions, though the whole thing is of course pretty Eurocentric. If you have the cash I'd say grab a new one and check the local used bookstores for a classic edition (and if you see something called the Wordsworth Dictionary of Phrase and Fable it is actually a reprint of the 1970 edition of Brewer's).