I've been meaning to reply to this one, because there are a number of books that I've come across that I think that folks on the forum might be interested in. Most folks have mentioned Animals of Farthing Wood, but there were seven other books in the series, a prequel and six sequels. Colin Dann also wrote quite a number of other animal books too - Just Nuffin, Nobody's Dog, The Ram of Sweet River, King of the Vagabonds and a few others. Just Nuffin and Nobody's Dog remind me of my own dogs (Just Nuffin because of the energetic antics of a young dog that get him into trouble and Nobody's Dog because my last two dogs including my current one are rescues dogs.
Garry Kilworth has written quite a lot of books from the point of view of 'realistic' animals - House of Tribes, Frost Dancers, Midnight Sun and Hunters Moon. He's also written the Welkin Weasels books, which fans of Redwall and the Wind in the Willows might like, only from the point of view of the weasels rather than the traditionally 'good' creatures.
There's the Ancient Solitary Reign and The Last Domain by Martin Hocke, a couple of books about owls - one from the point of view of Barn Owls, the other from the point of view of Tawny Owls.
David Clement-Davies wrote The Sight and Fell (about wolves) and Fire Bringer, a novel about deer.
Finally, there's William Horwood's books - The Wolves of Time, a series of two books, the Duncton Wood series and some sequels to the Wind in the Willows.
Sadly, most of them are out of print, but they are worth tracking down if you can get hold of them. Animal stories are a funny thing - there are quite a lot of them out there, but unless they are well known like WD, they aren't that easy to find since they were written 20 or more years ago and went out of print. I actually gave up on looking for books in the genre and started reading sci-fi and fantasy (as there's only so many times that you can read the same few books over and over again without getting bored with them) but still keep an eye out for ones I don't have or not read.
Edit: I forgot the Wild Road and the Golden Cat by Gabriel King.
Little Foxes by Micheal Michael Morpurgo.
Dot and the Kangaroo by Ethel C. Pedley.
The Hundred and One Dalmations by Dodie Smith.
Gobbolino the Witch's Cat by Ursula Moray.