This is sort of a different topic, but I've decided that I really like
www.aleks.com. It's a math curriculum site, and it's totally personalized to each student. The students have to fill in "pies" to complete each section, but they have choices about which pie slice to work on next. If they do well they move on, and if not they receive more instruction and practice. You can get a free trial, and then I think it costs $20 a month or so.
In the interest of full disclosure, my daughter has had no interest in trying it at all, but the school district where I work got it for a bunch of the kids who had trouble in math and some of them are really going to town with it.
dar