BookHooks – Online Book Report Publishing Center 
http://www.bookhooks.com/index.cfm

Spaghetti Book Club – Book Reviews by Kids for Kids!
http://www.spaghettibookclub.org/

Stories from the Web
Divided into a site for readers aged 8-11 or readers aged 11-14, this site has reviews by kids and excerpts from books.
http://www.storiesfromtheweb.org/sfwhomepage.htm