The three books that I think every library should have are Wombat Stew by Marsha K Vaughan, Doctor De Soto by William Steig and The Story of the Little Mole Who Knew It Was None of His Business by Werner Holzwarth.
I chose Wombat Stew because I discovered this story as a child and love reading it to my son. It has Australian animal characters and a song to accompany it.
The second story I feel should be in every library is another school favourite that I have passed to my son is Doctor De Soto. The story is about a mouse dentist who outsmarts a fox with a toothache.
The third book that I think should be in every school library is The Story Of The Little Mole Who Knew It Was None Of His Business, because what child and immature adult doesn't love a good story about animals and poop?! (pop-up version preferred!)