One Million Dots arranged in a grid format with gaps
ie the dots are arranged 10x10, then those are arranged 10x10, then those are arranged 10x10
It is possible to get this to print A4 / Letter so that all the dots show but it might take some
Poster showing the digits of Pi in a reducing font size (in an inverted triangle) so that it looks like they go on forever.
(Actually it's just over 700 digits)
A series of 5 posters showing some visually stunning examples of mathematics (with links for students to get more information)
Julia Sets
Koch Snowflake
Mandelbrot Set
Traveling Salesman Problem
Sierpinksi Triangle