Optical Illusions http://www.michaelbach.de/ot/index.html
Virtual Geometry http://nlvm.usu.edu/en/nav/category_g_4_t_3.html
Quilt Patterns http://www.alexandersonquilts.com/
More Quilt Patterns http://www.quilt.com/Blocks/AlphaBlockList.html
Some More Quilt Patterns http://www.quilterscache.com/QuiltBlocksGalore.html
Even More Quilt Patterns http://www.quiltbus.com/QuiltBlocks.htm
Still More Quilt Patterns http://blockcentral.com/blocklibrary.shtml