Many sites offer tessellation coloring pages, including Krokotak, Coloring Page Ed and Mom Junction. Additionally, collaborative websites such as Pinterest have countless tessellation pages available, often already sorted into collections by the site's social users.
There are also resources available for users to create their own tessellations. Shodor offers a simple creator involving a base shape, which the user distorts and pulls to her liking. Math Is Fun's "Tessellation Activity" allows free drawing that is replicated across a number of points on the page, allowing for less geometric creations. Tessellations.org is a great resource for information on tessellation artists and their methods/media, coloring pages, user-submitted tessellation art, stickers, paper-craft and more related material.