Beverly Cleary's Ralph S. Mouse series and her Henry Huggins books. Love the Mysterious Benedict Society. Hardy Boys/Nancy Drew mysteries. The Black Stallion books. Misty of Chincoteague books. Albert Payson Terhune's books about his collies, e.g. Lad of Sunnybank. James Herriot books. (I obviously got on an animal theme.) How about Encyclopedia Brown? Time Warp Trio. Mrs. Piggle Wiggle. The Great Brain. Last of the Great Whangdoodles. DD read some of these when she was 5-7.