For basic math skills and concepts, there is a great variety of free practice material available at Math.com and Coolmath.com. There are a plenty of interactive and concept presentation activities sorted by application.
Activities on the websites are tiered-lecture, practice and test formats, allowing the concepts to be rehearsed and students to become more comfortable. Each category on Coothmath.com carefully and colorfully explains the concept, breaking down each step to solve the problem. Each concept is broken down to a specific problem on Math.com. The concepts are built into units that tie each idea together with a unit quiz to review the materials.
Khan Academy has excellent interactive lectures and activities for all mathematics concepts from kindergarten through advanced calculus. The video lectures offered by Khan Academy are free, easy to follow and can be repeat as needed, and the lectures are more in-depth for each concept. The lectures are augmented by on-screen examples that can be repeated and move at a pace that allows all levels of understanding to follow along. Follow-up quizzes are available to test student understanding.
All three sites make excellent use of traditional mathematical learning patterns while taking advantage of online interactive technology and resources.