Can Teach
Can Teach: Math Centers
This page offers a variety of math center ideas for general math and geometry. Instructions on setting up the center are not provided for most ideas, however, those lacking instructions are pretty self-evident.
University of Cambridge
University of Cambridge: Nrich: Game Tantaliser Tantrix Discoveries
This game combines tangrams and pattern recognition to offer you a challenge. The page has a "Printable page" link if you want to print it out to help you work with the problem.