I fell in love with these stories as a kid, when different chapters were excerpted month by month into the Reader's Digest.
His first four books' titles are all lines from a hymn:
All Things Bright and Beautiful
All Creatures Great and Small
All Things Wise and Wonderful
The Lord God Made Them All
There was one more volume of entirely original material: Every Living Thing.
However, even before he passed away, his works were being packaged into a variety of books: Cat Stories, Dog Stories, Inspirational Stories, Best of Collections, etc. Some are collections of old and new, but some are just repackaged old stuff.
I treasure my Dog Stories, in particular the story of a dog named Clancy and an old man without adenoids; it proves that there's a right home for every dog!