http://wiki.apache.org/lucene-java/InformationRetrieval

Books

Introduction to Information Retrieval , Manning, Raghavan & Schütze, 2007
Managing Gigabytes [KevinBurton ] I can vouch for M.G. as I have a copy and it's a GREAT book. Should be called Managing Terabytes. Its not light reading by any means and you'll probably have to sit down with each chapter for a bit. ([DavidSpencer ] -- I agree, great thorough book, must have)
Modern Information Retrieval , Ricardo Baeza-Yates and Berthier Ribeiro-Neto, 1999
Foundations of Statistical Natural Language Processing , Chris Manning and Hinrich Schütze, 1999
Readings in Information Retrieval
Mining the Web - Discovering Knowledge from Hypertext Data by Soumen Chakrabarti , Morgan-Kaufmann. A good book that covers all the aspects of web and text mining.

Web links

Introduction to Information Retrieval , Manning, Raghavan & Schütze, 2007 This book is available online in PDF form.
Big list of links to IR resources: http://www-csli.stanford.edu/~schuetze/information-retrieval.html
Inquery Query help [PaulElschot ] This engine has a more elaborated query language than Lucene. However, Lucene supports most of the mechanisms used by the Inquery operators. Recommended: the section on Query Operator Types that makes the distinction between Belief List Operators and Proximity List Operators.
Course on Information Retrieval [JoaquinDelgado ] A very solid (and free) online course on "intelligent information retrieval" with focus on practical issues prepared by Prof. Mooney (Univ. of Texas), a well known expert in Machine Learning and IR.
http://finance.groups.yahoo.com/group/mg/
http://www.sims.berkeley.edu/~hearst/irbook/
course notes from the Stanford course on IR: http://www.stanford.edu/class/cs276/handouts/lecture1.pdf to http://www.stanford.edu/class/cs276/handouts/lecture16.pdf
http://www.dcs.gla.ac.uk/~tombrosa/AIS/SMART-tutorial/weights.html
http://trec.nist.gov/pubs/trec3/t3_proceedings.html TREC (Text REtrieval Conference) 3 Proceedings, including Salton's paper on SMART.
http://www.soi.city.ac.uk/~ser/idf.html The Spärck Jones / Robertson IDF page. Karen Spärck Jones is the author of the paper which introduced IDF.