4 Self-paced online Math curricula:
http://epgy.stanford.edu/http://www.aleks.com/http://www.mathletics.asia/http://uk.ixl.com/ALEKS has a free trial.
http://www.aleks.com/free_trial 2 months for parents, I think less for teachers. I used the free trial. My children are 7 and 5. Both were able to progress through their Grade 3 modules in about 30 hours of effort. Not sure if my kids are brilliant or the material is easy or both. The material seems comprehensive though. The software requires you to mess around with java but once its running, it does a good, workmanlike job of presenting and explaining the topics.
I have only had brief exposure to Mathletics. It seems more oriented towards the teacher assigning work. The put a lot of work into animations and the kids seem to like it. At first blush it seemed either too easy or too hard, not tuned to a middle ground. Also has a feature of competition with other kids, live, worldwide.
I am even less qualified to judge EPGY. It seems well regarded, more expensive, and correct me if I'm wrong but seems bound to a particular schedule.
Would love to hear from other parents who can compare the above. Will search for existing discussion threads.
