I really like the Ramona Quimby books by Beverly Cleary. I think the Mouse on the Motorcyle series is good too for that level. My upper level girls like the American Girls Series.One year my really good readers liked the Hank the Cowdog series. There is so much out there it is hard to pick!
I'm sure your librarian would be able to help you.
Some that I know kids really like are the Bailey School Series with titles like Mummies Don't Coach Softball, Leprechauns Don't Play Basketball, etc. Also, the Cam Jansen series of mysteries are good. Nancy Drew has a series called Nancy Drew Notebook which are chapter books.