PHP
Professional PHP Programming (Wrox) (first PHP book that I bought)
Programming PHP (O’Reilly)
Web Database Applications with PHP and mySQL (O’Reilly)
Object-Oriented PHP (No Starch Press)
Latest additions:
Advanced PHP Programming (Developer’s Library)
CodeIgniter (Wrox)
Professional Search Engine Optimization with PHP (Wrox)
PHP Cookbook (O’Reilly)
PHP Objects, Patterns and Practice (apress)
php|architect’s Guide to PHP Security (php|architect’s)
php|architect’s Guide to Date and Time Programming (php|architect’s)
Essential PHP Security (O’Reilly)

Javascript/AJAX:
Javascript The Definitive Guide (O’Reilly)
AJAX The complete Reference (Mc Graw Hill)
Professional AJAX (Wrox)
Javascript: The Good Parts (O’Reilly)
Dojo: The Definitive Guide (O’Reilly)
jQuery: Jquery Novice to Ninja (Sitepoint)

mySQL
mySQL and Perl for the Web (New Rides)
MySQL (Developer’s Library)
High Performance mySQL (O’Reilly)

Perl
Perl Cookbook (O’Reilly)
Perl for Web Site Managers (O’Reilly)

Other languages
C# 2005 (Wrox)
ASP.NET 2.0 (Wrox)

XML
XML A Beginners Guide (Mc Graw Hill)
XSLT (O’Reilly)

Other
Web Form Design (Rosenfeld)
Apache 2 Pocket Reference (O’Reilly)

OS:
Ubuntu: The OS of choise. Although I might return to Windows because there are tools there that I find better. (Photoshop, Visual Studio, InDesign, Illustrator, PHPed… and the list continues)

Main development tools:
Editor: Komodo IDE 5.X … or Aptana Studio Professional
Browser: Firefox (But I have to test on other browsers as well…)
vmWare: for testing on Safari and Internet Explorer under Windows. (Currently not installed after upgrade of Ubuntu)

Languages:
PHP – This is my main development language, but I also do write ASP.net/ASP on occasions.
Perl – This language comes into use when PHP is limited (like on uploading big files)
Javascript – Used to enhance the user experience for the application. I have now started to use jQuery.

Other Tools:
Inkscape: To create graphics.
Gimp: To edit pictures – although I really, really, really don’t like the program as I am more familiar with Photoshop. I have looked at a program called Pixel which seems promising.
Komodo IDE: This is the editor I use at the moment. I have even paid a license for it. I am considering Zend for Eclipse, but I find the fee rather high. I know that under Windows I wouldn’t mind paying for it, but under linux I think I find Eclipse a tad bid unstable… (or am I wrong – prove me!)
Aptana Studio Pro: I am switching back and forth from Aptana and Komodo. There are some things that I like about Aptana and there are things that I like about Komodo. The latest is faster, but I am missing a few things. One thing is the Tasks “window”. It is in Aptana (and in Netbeans – where I first saw it – and probably also in Eclipse since Aptana builds on Eclipse). I do wish that the Aptana developers did something to the task-window as I would very much like to see only the tasks that are at hand in the file that I am working in – or in the files that I have opened at the current time.