Venture into a fantasy world as told through the eyes of animals - Mostly feral with some light anthropomorphic novels.
The criteria used is pretty light: it must be a book (not a comic) and the main character must be an animal (there's some leeway here, though). Sci-Fi novels that use animal-like aliens or humans transformed into animals are excluded since they're not very "animal".
I encourage everyone interested in this theme to recommend books for the list and submit blurbs for the book you have read explaining why its a good book (or why its not).
The books are ordered by the number of books in a series/same author. Other than that, they're not prioritized in any other way.
Thanks to Zabdiel for recommending the Duncton Woods series.