There is always a great selection at Whitcoulls Botany. One thing I love about this store is the clear distinction between the ground floor and the floor above. Anything kids-related - top floor; anything else - ground floor. Makes my shopping a lot easier
This is one of the last standing large bookstores, with a huge selection of books and a large childrens section upstairs with puzzles and games etc. Unfortunately I've noticed the range of books dwindling and the prices of books here can't really beat online book stores, so it may only be a matter of time before we lose this bookstore too.