Kunst-Formen der Natur (Art Forms in Nature), by Ernst Haeckel, 1898. This is a wonderful book, in the public domain, which features all sorts of illustrations of the natural world
providing commonly used dimensions, based on a width of 960 pixels / two variants: 12 and 16 columns
A toolbox of several Web widgets and APIs originated from the MIT Simile project.
It offers an interface to Yahoo! and Google, but with two notable improvements: an excellent logging/data retention policy, and a feature that shows the user information about sites' privacy policies along with the search results