Love You Forever, Robert Munsch
No Dragons for Tea, Jean Pendziwol and Martine Gourbault (a fire safety book, the whole thing rythmes it's really cute)
Alexander and the Terrible, Horrible, No Good, Very Bad Day, by Judith Viorst and Ray Cruz
The Hockey Sweater, Roch Carrier, Sheldon Cohen, and Sheila Fischman
and all the Shel Silverstein poetry books are an excellent introduction to poetry for kids. My kids were that age when I bought them for them (because they were my favorite when I was a kid) and they still love those books, as teens. They encourage reading because they can read a short poem then you read a long one, they're funny and weird and well...every home library should have them.