Information Architecture is the way content is structured on a web page. It comes in many forms such as: All-in-one, flat, hub-and-spoke & daisy, strict Hierachy, mulit-dimensional hierachy, and search.
Examples of web sites using the IA Models:
Flat: Neaopets
Daisy: Hotmail
Strict Hierarachy: Hoyts, Bom, Blizzard
Multi-Dimensional Hierarachy: Amazon
Search: Google, Yahoo, Ask Jeeves, Ebay, Wikipedia, TorrentSpy, Wombat, Sensis
