Chinese Abacus - cross curricular history and math lesson. Place values, addition & counting. This site has a good explanation of the history and use of the abacus. Pretty cool and hands on idea for supplementary math instruction.
This interactive CCSS-aligned SMART Board lesson on Number Representation & Place Value gives students an interactive and hands-on approach to learning about place value and how numbers can be represented in different ways (standard form, expanded form, and word form). Lesson includes an interactive 'Match It!' game, interactive 'Test Prep', interactive place value blocks, 'Writing in Math' problems, and Math Journal prompt slide to assess what students have understood after the lesson.