Absolutely second The Last of the Really Great Whangdoodles -- one of my favorite books of all time, even now! Some other really excellent ideas above.
How about Beverly Cleary books? Ramona is very popular now with the advent of the new movie, and there are several books about her. Also Henry and Ribsy, and Ralph the Motorcycle Mouse.
The Shoes books are excellent and I always loved them, still do. Ballet Shoes, Theater Shoes, Skating Shoes, Circus Shoes, etc., by Noel Streatfeild.
Paddington books are good as well, and the Tee-Bo series about a talking dog, and the Moomintroll books.
I can't wait till DD5 is old enough for some of these -- they're all sitting on her shelf or in boxes, waiting for her interest to catch up! :-)