Search Engines: Information Retrieval in Practice (Bruce Croft, Donald Metzler, and Trevor Strohman; University of Massachussets at Amherst). Java-based Galago search engine code referred to in the text can be found here.
Introduction to Information Retrieval (Christopher D. Manning, Prabhakar Raghavan and Hinrich Schütze; Stanford University, University of Stuttgart, and the University of Munich)
Writing for Computer Science, 3rd edition (Justin Zobel)
The Elements of Style, 4th edition (Strunk and White)
The Sense of Style (Stephen Pinker)
Evaluation Tools
trec_eval: standard tool used for evaluating retrieval effectiveness in international competitions (e.g., TREC, NTCIR, CLEF, FIRE). This is the official C implementation version 9.04.