Totally Tessellated Click on the History, Essentials, Mosaics/Tilings, Escher, and Beyond links at the top of the page. http://library.thinkquest.org/16661/index2.html
The Mathematics Behind the Art of M.C. Escher http://www.math.nus.edu.sg/aslaksen/gem-projects/maa/0203-2-03-Escher/main.html
Making a Fractal http://math.rice.edu/~lanius/fractals/
Geometric Designs in Islamic Architecture http://www.islamicart.com/main/architecture/geometry.html
Tessellations in the World Discussion -- Check here for famous places to research http://www.shodor.org/interactivate/discussions/TessellationsWorld/
Alhambra, Spain -- Check out the images on this page! http://en.wikipedia.org/wiki/Alhambra#A_tour_of_the_Alhambra
Lava makes tessellations too (although not perfect!) http://en.wikipedia.org/wiki/Giant%27s_Causeway
Tessellations in Science & Nature -- Scroll down to the links under "Activity 16" http://britton.disted.camosun.bc.ca/jbsymteslk.htm