FreeTechBooks.com, a site which lists “free online computer science and engineering books and lecture notes” has an article about a data mining book: Data Mining – Desktop Survival Guide. It is written by Graham Williams working at Togaware.
The book provides a practical guide to doing data mining. Covered audience is mainly the information technology worker, the software engineer, and the data analyst. One particularity of this book – except the fact it is free – is that it avoids going into too much details of data mining techniques.
This book covers basic area such as decision tree induction, association rules, multivariate adaptive regression splines, patient rule induction methods, etc. The language chosen to illustrate algorithms is R. For more detail about this language, I refer you to an older post of Data Mining Research. This book is freely accessible here.