Wolfram Research
Wolfram Math World: Semiregular Tessellations
This one page Mathworld site has a number of examples of semiregular tessellations. A definition and a small amount of related information is given at the bottom of the page.
ClassFlow
Class Flow: Tesselations
[Free Registration/Login Required] This is a visual instruction of tessellations. It displays a variety of tessellations throughout the world and in different cultures.