Book recommendations - 3rd/4th grade reading level?

I teach students who are special needs ESL kids. They are in 6th and 7th grade, reading on a 3rd to 4th grade reading level. I have been given funds to buy cl sets of books. I want to avoid books with too many illustrations or that may be too babyish. Harry Potter is too hard for them. I'm thinking of the following titles: Encyclopedia Brown, The Littles, and Pippi Longstocking. Any elementary or middle school librarians out there who can recommend more titles?