In most cases, directions are included on how to make your own sets of pieces as well as problems to work on. Classroom Connect formerly Ed's Oasis Treasure Zone lets you know about sites that are interactive or full of extensive information. Just use the search function for math lessons. PrestonSpeed's Navigate the Net Math Page offers some great links for teaching math. Natural Math is a more natural approach to math.
Topics range from simple addition to an introduction to functions.
Math has lots of lesson plans aimed at elementary aged children. Science Help Club is for people who need help, want to give help, or want to help us all by asking intriguing questions and starting great discussions about math and science. Sumfun is an interesting list of math links. BasketMath allows you to shoot the a basket every time you solve a problem correctly. Edmark's Mighty Math Club Just started to highlight their new series of math games.