I myself bought "PHP, MySQL and Apache All in One" by "Meloni". Nice book, but I actually never used a book for PHP...pretty self explaining (especially with tutorials). I always used it to look up MySQL data types and / or commands since the MySQL site's reference is an absolute mess, IMO.
Generally, when I use a language sporadically, I buy a book, since I can't remember the function names / parameters, lol. I did bought a book for C, but I barely use (I love the reference part though)...however, ASM is just too complicated (if you include all explanations on how the hardware actually WORKS ;-))...getting off topic.