K5 Learning has an online reading and math program for kindergarten to grade 5 students. I've been given a 6 week free trial to test and write a review of their program. If you are a blogger, you may want to check out their open invitation to write an online learning review of their program.
As an added note (after the required disclaimer) I am very excited to be trying this program specifically for Caleb. This opportunity came to my attention at just the right moment because we have been looking to find a supplemental, ideally computer based, program to give him more practice without mom sitting with him. He sits well for lessons but not so well for continued practice.