World of Escher
MCEscher.com, the ‘official’ Escher site. Not really overwhelming, sorry.
Escher’s World has several Java applets of tesselations that you can change by clicking and dragging with your mouse.
World of Escher – The Site for Everything Escher “are proud to be here to tell you stories, discuss M.C. Escher’s works, provide insight, and offer our high quality products promoting the intriguing work of Escher. […] Along with discussions on Escher we have also included ideas and readings regarding Professor Roger Penrose and his mathematically based puzzles.”
M.C. Escher Centennial Celebration Page. “M.C. Escher has fascinated young and old with his unique interpretation of the world around us in his drawings and prints. From impossible worlds to repeating pattern tessellations, Escher shows us the unique harmony and beauty that are in simple things in our surroundings. This site is a celebration of the Centennial of M.C. Escher and contains information about exhibitions, educational resources, and links to other Escher sites.”
Escher Gallery at the National Gallery of Canada
Escher Gallery (page 1 of 8) at the National Gallery in Washington, USA.
Escher Art Collection which also includes a few works after Escher.
Kyle’s Personal Asylum. A collection of Escher’s work.
Escher Wallpapers, a collection of desktop pictures.
Math and Teaching
Teaching Escher: Using Escher in Classrooms. “This page is a resource for those who are interested in teaching about Escher and integrating his artwork into a school curriculum. Escher’s art captivates young and old and is a fun and educational way of learning about art, mathematics, and sciences.” (Part of the Escher Centennial Celebration page, see above.)
Example: Model Unit (Grade 7): M.C.Escher: The Poet of the Impossible.. “In this unit, we see integration of two subjects (mathematics and visual arts) with the concrete (the art of M.C. Escher).”
For reading about M.C. Escher and his artwork, I recommend Bruno Ernst: Magic Mirror of M.C. Escher, ISBN: 1886155003. (Oder auf deutsch: Bruno Ernst: Der Zaberspiegel des Maurits Cornelis Escher. ISBN 3822889474.)