Amaya has been progressing nicely over the years and supports HTML, XHTML, MathML 2.0, SVG (even transparency and animation), and much of CSS 2 ... You can display and somewhat edit XML ... and there's some powerful tools for live editing...
The JetBrains Web IDE is a new Integrated Development Environment for web programming: Html, CSS, Javascript, XML, PHP, and SQL ... and support for version control systems, etc
Build-time error reporting, refactoring and code completion in Visual Studio
Extended JavaScript syntax power with C# language features
Pure client-side control library coded in C#