One of the better values found on the Internet are the free textbooks listed below.
The Weblinks Collection
Electronic Statistics Textbook *Nicely done and very extensive online stat textbook from StatSoft. Covers most major statistical areas and include good graphics. Best of all its free!
HyperStat *Another good and free online statistics textbook.
Research Methods Knowledge Base *While this site is a slightly scaled-down version of a printed textbook the material is still quite strong and should serve as a very good primer on how to conduct business and social research.
Sales Management *Prof. Charles Futrell has been writing sales textbooks for many years and now his textbook on sales management is freely available in PDF format. The book has 16 chapters and covers all the major issues in managing a sales force.
Sports Marketing *Technically this is not a book but summaries of chapters from Matthew Shank's book. Also includes Internet exercises.
Warehouse & Distribution Science *Authored by John J. Bartholdi, III and Steven T. Hackman from Georgia Institute of Technology. this books provides good insight into what is involved in moving and storing product. Link provides information for accessing book and also instructor materials