Practice your grammar skills. http://www.eduplace.com/kids/hme/k_5/quizzes/
A lot of sites on reading! http://jc-schools.net/tutorials/interactive.htm#Reading
This site is all about reading and writing. There are word games and even instructions on how to write and publish your own book. http://library.thinkquest.org/J001156/index.htm
Here's a fun game about types of sentences. http://www.harcourtschool.com/activity/clubhouse/index_pre.html
To find a list of appropriate books for the fourth grade, click here. The list is organized by favorites, independent reading, and nonfiction. Guided Reading levels are shown. (You will need Adobe Reader for this one.) http://teacher.scholastic.com/products/paperbacks/pdfs/Ready-To-Go_Grade_4.pdf