How Search Works by Matt Cutts -- a look at how Google selects what sources to give you in response to your query, and how the results are ranked.
Web Search Strategies in Plain English by CommonCraft -- great overview, with an introduction to the concept of predictive search.
Bergson-Michelson, Natasha. “Predict Before You Click.” Knowledge Quest (Jan./Feb. 2010) Vol. 38, No. 3, p. 8-13. -- A detailed look at how to teach students to select which links to click on from a search results page.