Buy this bundled with the above and they both then easily justify their cost.

Perfect partnered with the above, this is also one of those subjects that people don't explain they just tell you to turn it off.

Mines on order at the moment.

This covers slightly more diverse subjects and probably isn't needed for the hobbyist/home user, but for the professional it's got some of the less covered subjects.

Where to start with MySQL, I own an old version of this book and it covers everything.

How to tune your MySQL databases to the bleeding edge, covers everything with decent detail and explaination.

This is the place to start for PHP (apart from the PHP site obviously), I've got an older version but these books cover the starting ground comprehensively.

The Perl Cookbook, good recipies for good solutions.

The cookbook partner to the above, the only reason it's not on my wishlist is because I do this stuff before I have breakfast, litterally sometimes.

This isn't going to make you a web developer but I really wish people would stick to the absolute highest standards and to do that you need to know the whys, hows and whats. So this book makes it in.

Some of the examples are dated but the lessons remain, if you manage anyone in any IT project based capacity and you haven't read or heard of this book then you need to read and digest this.