I prefer to send people to amazon and its related sites for people to purchase technical books for their great prices, ranking and review system, and international presence. Outside of amazon, I would recommend the following places:
This is the "bookstore" that my team maintains. We choose a new title roughly every month and usually link from the book to amazon.com.
This is the site that is maintained by IBM and is updated with the latest on the IBM Press books that are available.
This is the site that our publishing partner, Pearson Education, updates. From here you can get a newsletter, purchase books, get chapter downloads, and more. Quite often we'll point to this site if we have an electronic coupon that we are promoting.
If you DO NOT reside in the US and would like to purchase books in your local currency with lower shipping costs, use this link. From here you can get to our Canadian http://www.pearsontechnology.ca/DB2/ or European http://www.pearson-books.com/ibmpressbookshop/ IBM Press pages. We've also listed the books that are available in translated or low cost editions with details as to how you can order them.
5) http://safari.informit.com/ or http://www.books24x7.com
For electronic versions of books see either of these sites. IBM employees have a subscription to books 24x7, but many universities, colleges, and business have a subscription to Safari. Both engines allow individual subscribers as well.
If you work for IBM, go to this site for details on how to access employee purchase sites.
I'd like to say that you can also buy technical books in bookstores, but this is usually only true for mass appeal books. One day I hope that DB2 books move into this category!
If you have another favourite place where you buy books, share your information.