On trainings I run for practitioners teaching literacy I am increasingly being asked about maths teaching. I recommend two materials' sites. The first, for young children, is the Schofield and Sims website and their Mental Maths series. My youngest daughter benefited hugely from doing three or four of these exercises every week throughout the primary phase, so much so that she was streets ahead of most other children by the end of Year 6. The second is the Ichthus Resources site, which sells Singapore Maths books. The Singapore Maths books are amazingly comprehensive and teach fundamental concepts and facts, as well as providing loads of practice.
Picture thanks to http://www.stjosephsbns.ie/images/maths.gif