We've tried Time4Learning.com in the past - we cancelled it when it didn't get enough use. I'd consider trying that again if it's considered the best. Part of the reason it wasn't used was busy life at the time.
We also have ixl, which is a math program. While it isn't fancy, it is nice for doing assessment- Once the children have covered an area, we log onto ixl and have them do the problems there to see if they transfer learning and see what their understanding of the content was.
We love brainpopjr and use it several times a week.