“Information Architecture for the World Wide Web” is considered one of the definitive books for developing usable, intelligently laid-out, easy-to-use Web sites. Peter Morville and Louis Rosenfield wrote the first edition in 1997 and it aged exceptionally well, even with the break-neck speed of technology. I read it in 2001 and everything in it was just as applicable then as it was when it was written four years earlier.
The second edition of the book has just been released, and O’Reilly has published Chapter 8 in PDF format online. The chapter explains search systems and lays out the lessons and rules that make one search engine succeed where others fail.