Cut the Knot
Cut the Knot! Pick's Theorem
This site explains Pick's Theorem and contains an interactive geoboard and activity to help understand the theorem.
University of Cambridge
University of Cambridge: Nrich: Virtual Geoboard
Use this virtual geoboard to explore the attributes of various polygons. This would work well on an interactive whiteboard.
National Council of Teachers of Mathematics
The Math Forum: Using Geoboards in the Classroom
A thorough look at the extensive uses of geoboards in the classroom. Links are listed which give introductory information on geoboards - for teachers new to using them. Then, lesson plans are provided for using geoboards in teaching...
University of Waterloo (Canada)
University of Waterloo: How to Use the Geoboard
Four worksheets are linked which deal with area and perimeter of shapes constructed on the Geoboard. Additionally, a link is given to an online Geoboard so students may play with the model on their own.