http://nlvm.usu.edu/en/nav/vlibrary.html
If you are an educator, you know what it is like to search frantically for lima beans and spray paint on a Sunday afternoon or to call around searching for a complete set of geoboards on a Tuesday morning. Manipulatives are often few and far between and sometimes require an art degree to create on your own. Thankfully, with a computer, an internet connection, and a java-enabled browser, these priceless tools are now at your fingertips.
The National Library of Virtual Manipulatives (NLVM), started in 1999, serves as a virtual library of interactive, web-based virtual manipulatives for mathematics instruction. NLVM offers manipulatives in Number and Operations, Algebra, Geometry, Measurement, and Data Analysis and Probability. It is organized by strand and grade level for quick and easy searches.
The library is comprehensive including hundreds of resources for every subject, concept, and skill. You can use NLVM to enhance their mathematics classroom and actively engage children. The manipulatives help children visualize mathematics relationships and concepts. To view the manipulatives you only need a computer with an internet connection and a java-enabled browser.