Interactive Base Ten Blocks
This interactive whiteboard tool lets children explore place value and two-digit (grade 1), three-digit (grade 2), or four-digit numbers (grade 3) using the traditional base ten blocks. You can either drag different place value units (ones, tens, hundreds, and thousands) onto the whiteboard, or choose "Automatic" to let the computer give you a random amount of blocks. Push the "total" button to reveal the total.
This activity works great both for students to practice place value concepts and for a teacher to illustrate them to the whole class. It suits best grades 1-3.