It is always a challenge to find books for the 2nd through 5th grader with a high reading level. I always try to find novels where personification is used and the main characters are animals. Those books usually have appropriate content, rich language, and strong themes. This website includes some specific examples of higher level books with appropriate content.
http://www.multcolib.org/kids/booklists/readingup.html
http://www.multcolib.org/kids/booklists/readingup.html