We've tried EPGY, ALEKS, IXL, and Khan Academy, and Khan Academy is the hands-down winner in our house. The teaching style in the videos is IMHO more enjoyable than with EPGY, and DD really likes that she can choose what she wants to work on. The drawback is that it's not linked to any state standards, so you have to choose your own adventure. IXL was too much of the same - 10 perfect problems in a row, with the opportunity to earn a badge by doing more, is a more-tolerable level of exercise repetition.
I've been doing some Khan Academy, too, and have determined that DD's propensity for careless errors probably comes from me.
