There is a great series of books called Secrets of Droon. My kids for the last 3-4 years have LOVED them. They are very similar to Harry Potter. They are a 3rd grade rdg level. I use them mostly to enjoy as a read aloud, but have used them for teaching vizualization and other comprehension skills and also writing skills. The author is Tony Abbott. He writes wonderful descriptions. I can't say enough about these books. It's the only thing that settles my kids down at the end of a hectic day!
You forgot 2 fabulous ones! My class is nuts about Franny K. Stein books--they are easy independent reads, and really encourage an excitement about science. Another great one is Stink by the author of the Judy Moody books. Stink is Judy's little brother in 2nd grade, and the book is right on level for 2nd graders.