1. Aptana Studio 3 by Appcelerator, Inc
Platform independent as the IDE runs on Java JRE and supported programming languages are HTML5, CSS3, JavaScript, Ruby, Rails, PHP and Python.
Aptana Studio 3 is currently release under “GNU General Public License“.
2. Adobe Dreamweaver CS5.5 by Adobe Systems
Favourite by large web development firms. Runs on mac osx and windows platform. Supported programming languages are HTML5, CSS3, JavaScript, PHP, ColdFusion Markup Language (CFML) , VBScript (for ASP), C# and Visual Basic (for ASP.NET) and JSP. Commercial license required to install and use.
3. Eclipse by Eclipse Foundation
Open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle. Platform independent as the IDE runs on Java JRE. Download the Eclipse PDT package for PHP support. Currently release under “Eclipse Public License (EPL)“.
4. Zend Studio 8 by Zend Technologies Ltd
According to their FAQ, Zend Studio is a commercial IDE with rich a feature set including remote debugging, Zend Server integration, Zend Framework support, and more. Supported programming languages are HTML, CSS, JavaScript and PHP. If your presentation uses JavaScript libraries such as Dojo, jQuery, Prototype and Ext JS, then you may want to consider Zend Studio as it comes with content assist for the libraries. Zend Studio 8 runs on linux, mac osx and windows. Commercial license required for use after 30 days evaluation.