Aptana Studio 3.

It may seem odd, but the first item in our list isn’t a WYSIWYG editor at all. Aptana Studio is an “open source development tool for the open web” which, in practice, means it’s more of an advanced IDE specializing web development. Based on the open source Eclipse project, Aptana Studio features tools for assisting in HTML and CSS authoring, including code coloring and completion, debugging, and outlining of documents. Its main selling point is its JavaScript support, making it a strong tool for developing more complex web applications.

http://www.aptana.com/