Hash Validation Tools

• HashTab - Windows/Mac tool for validating MD5/SHA1 hashes of downloaded files

PHP, HTML and Text Editors

Freeware

• Notepad++ **RECOMMENDED**
• Aptana (an Integrated Development Environment for Win, Mac and Linux)
• NotePadXP
• Arachnophilia (allows GUI design of HTML)
• Crimson Editor
• Nvu (allows GUI design of HTML)
• PHP Editor
• Win32Pad
• PSPad
• TextWrangler (Mac)

Commercial

• BBEdit (Mac)
• TextMate (Mac)
• TextPad
• Namo WebEditor
• Dreamweaver (allows GUI design of HTML)
• Zend Studio Designed for PHP editing by the authors of PHP

CSS Debuggers

• Firebug Is the most popular useful tool for working out CSS and Ajax/Javascript problems on your site.
• Firefox with the Web Developer Extension
• The latest versions of the more popular browsers also have built-in "Inspect Element" functionality, which can significantly aid in troubleshooting.

CSS Editors

Freeware

• See Firebug and the Web Developer Extension in the CSS Debuggers section above for the best tools available!
• CSS Tab Designer (only for building CSS tabs)

Commercial

• BBEdit (Mac)
• TextPad
• TopStyle Pro

Text-Search Tools

Freeware

• Crimson Editor
• PSPad
• TextWrangler (Mac)

Commercial

• BBEdit (Mac)
• Funduc
• HandyFile
• TextMate

Graphics Editors

Freeware

• GIMP (Win/Mac/Linux)
• IrfanView
• Photo Plus
• Photofiltre
• Photomeister
• Paint.NET

Commercial

• Corel PaintShop Photo Pro
• Acorn Image Editor (Mac)

Screenshot Tools

Freeware

• IcoMaker (Mac)
• IrfanView
• Pixen
• PrintScreen
• Screen grab! (Add-On for FireFox)
• Awesome Screenshot (Add-On for FireFox/Chrome/Safari)

Commercial

• Little Snapper (Mac)
• Fireworks
• Flash
• Snapz Pro X

Color Pickers

Freeware

• ColorZilla (Add-On for FireFox)
• Color Pix (Windows, Mac)

Commercial

• ColorSchemer Studio (Windows, Mac)

File Comparison Utility

Freeware

• WinMerge (Windows)
• FileMerge (part of Apple XCode tools) (Mac)
• TextWrangler (Mac) (TextWrangler has built-in basic "Find Differences" tool which is faster than FileMerge)

Commercial

• BBEdit (Mac)
• Beyond Compare (Windows and Linux) ** Offers 3-way comparisons! **
• DeltaWalker (Windows, Mac, Linux) ** Offers 3-way comparisons! **
• DiffFork (Mac)
• Guiffy (Windows, Mac, Linux) ** Offers 3-way comparisons! **
• Araxis Merge (Windows, Mac) ** Offers 3-way comparisons **
• Kaleidoscope (Mac)

FTP Tools

Freeware

• WinSCP A great Windows-based secure-FTP program. *RECOMMENDED*
• FileZilla (Windows and Mac)
• FireFTP (Add-On for FireFox)
• FlashFXP
• CyberDuck FTP (Mac)

Commercial

• Transmit (Mac)
• BBEdit (Mac)
• WS_FTP Pro (Windows)
• Zend Studio (Windows/Mac/Linux)

File Archiver/Zip/Unzip Utility

Freeware

• 7-Zip
• IZArc

Commercial

• WinRAR
• WinZip

Browser Addons/Utilities

Freeware

• FireBug (Add-On for FireFox)
• Aardvark (Add-On for FireFox)
• BBCodeXtra (Add-On for FireFox)
• CoLT (Add-On for FireFox)
• CSSViewer (Add-On for FireFox)
• HTML Tidy (Add-On for FireFox)
• Selenium IDE (Add-On for FireFox)
• SourceEditor (Add-On for FireFox)
• View Source Chart (Add-On for FireFox)
• Web Developer (Add-On for FireFox)
• JSView (Add-On for FireFox)
• Safari WebDevAdditions

Validators

Freeware

• CSS Validation Service
• W3C Markup Validation Service

Database Manipulation Tools

Freeware

• phpMyAdmin
• SQLyog

Commercial

• SQLyog
• Navicat

Local Web Server for Development Environment

Freeware

• XAMPP
• MAMP (Mac)

Other things

Freeware

• Wink - a Tutorial and Presentation creation software for windows

External Resources/Tutorials

• MySQL
• php.net
• SitePoint.com
• Tizag.com
• W3 Schools
• Clean CSS Online tool to optimize your stylesheet
• CSS Formatter and Optimiser Online tool to optimize your stylesheet.