Most people know buying books online is cheaper than from a local bookstore. But not many people know Amazon.com is not the most inexpensive place to buy computer books. Once in a while I compare book prices at the following online booksellers
A1Books
AltBookStore
Amazon
BarnesandNoble (a.k.a Book.com or Books or Fatbrain)
Bookpool
Borders
Booksnow
CDParadise
Quality
Amazon, Barnes and Noble, and Bookpool allow you to write book reviews. But Amazon has the lion share.
I wish I had time to get actual statistics but I only have an impression. That is, O'Reilly and Addison-Wesley are consistently acclaimed as decent publishers in the computer professional community. Other good publishers are Oracle Press (Oracle books only), Prentice Hall (PTR) and Wrox. On the other end, books often seen stay long at Half Price Bookstores in the Houston area are published by Macmillan's New Riders, Que (it went under!) (It would be nice to write a program to automatically collect the data of star rating on Amazon).
Be cautious about bogus readers' reviews or sham reviews. The Black Book series from Coriolis is a typical example (the site is no longer a book business). The readers may be paid by the publisher or the author and submit reviews with different identity. Particularly worthy of mention is the guy named <identity given on request>, who posted dozens of 5-star short reviews on books published by the infamous Coriolis, using words such as "best", "only", without going into details, including a book he coauthored and I happened to read "Oracle Databases on the Web", one of the worst computer book I've ever read. Then he went on to write "Oracle SAP Administration" for O'Reilly! I haven't read this one yet so no comment. But readers who often commented on his own book with short sentences rating 5-star either didn't leave email addresses or with addresses from the wildcreek.com domain. I emailed one of the wildcreek reviewers pretending to solicitate more comment but never got replies. (For more details about this investigation, view source of this web page you're reading.)
More objective reviews will be from the revelant newsgroups. If you post a question "Anybody thinks such and such a book is good?" or "Can anybody recommend a good book on...?", you'll usually get quite a few replies. Since these questions are frequently asked, you may directly go to the FAQ for this group at MIT FAQ Repository. But most FAQ authors only list good books even without comments. Some groups, however, have excellent (albeit prejudiced thought by some), book critique. Tom Christiansen used to have Camel Critiques on Perl books and Elliotte Rusty Harold's Java Book List.
Appendix
Yong's Book Reviews Some of them were written during tens of hours of careful investigation, experiment, and cross-reference.
To my Computer Page