New Edition on William Street in Northbridge has an incredible number of fantastic books, floor to ceiling. A lovely shop, such a wide variety of subjects, and some beautiful hard cover collectors items. They also make a mighty fine coffee!
Also the one in Nedlands, near Broadway -though cannot remember the name -they have all old books and I once bought one there for $250 -it is a very old Peter Pan -I used to collect old children's books and have a beautiful cabinet full.
I was just in Elizabeth's Secondhand bookstore on Hay Street in the City today, and it's really lovely. While they mainly have secondhand books they also have a good selection of new titles as well, beautiful children's books, collectible comics and antiquarian books. There are several shops around Perth...in the City, Subiaco and Fremantle. Apart from all the wonderful books you can find there, they're always very atmospheric with lots of cool props and decorations scattered here and there.