Rep-Tiles are tiles of a particular shape such that duplicates of a shape can be combined to form a larger version of the same shape. The website has 7 different Rep-Tiles to choose from.

Instructions
http://www.teacherled.com/2009/01/19/rep-tiles/

Resource
http://www.teacherled.com/resources/reptile/reptileload.html

Worksheet, so students can solve the puzzles at their desks
http://www.teacherled.com/resources/reptile/reptiles.pdf