This is a useful maths site for teaching place value to young children with virtual hundreds, tens and ones blocks.
http://ictmagic.wikispaces.com/Maths
Great multipurpose maths thinking blocks. Add different colour blocks, change their size and break into fractions. Click the 'problems' button and give lots of maths questions to work out with the blocks.
http://ictmagic.wikispaces.com/Maths