Melissa Taylor of the Imagination Soup blog recommends some picture books and easy chapter books for beginning readers. You can view her list and short reviews at Summer Book List for Beginning Readers. Many of these books are the latest in a series, so that gives you even more book ideas to help prevent summer brain drain in your beginning reader.
The Sonoma County Library has several copies of Nancy Clancy, Secret Admirer as well as several copies of Nancy Clancy, Super Sleuth. The Library also has the following books: Critter Club, Amy and the Missing Puppy, Swamp Thing vs. the Zombie Pets, Amelia Bedelia Unleashed, Mermaid Tales, Battle of the Best Friends, Zeke Meeks vs. the Stinkin' Science Fair, a truly horrifying tale Zeke Meeks vs. the Horrifying TV Turn-Off Week, Pinch and Dash and the Terrible Couch and A Trip to the Bottom of the World.