Buying computer books is a bit of a waste of money since their information is relatively out of date in a couple of years. So recently I purchased some of sitepoints books digitally when they went on sale. I find it difficult to thumb through a digital file (pdf) when I want to look up something. It is much easier to search the internet.
However there are always exceptions. I have recently purchases Ben Forta’s Coldfusion 8 Web Application Construction Kit volumes 1 and 2. There is so much information in there about building CF applications that it adds to my foundation of general knowledge. There is so much material and examples as well as various methods for using coldfusion that anyone should benefit from these books. I recommend you buy them used for more than half off. You can click these links to buy or review them:
Adobe ColdFusion 8 Web Application Construction Kit:
Volume 1 – Getting Started | Volume 2 – Application Development
I also like my old PHP 4 books. I have 3 different levels of them from basics to advanced techniques. I refer to them again and again.
My books for FLASH, Dreamweaver, Photoshop, and other software packages are the ones that get used the least and are out of date the fastest. They look good on my desk shelf and let people around me know what I do.