The Expression line of applications are a suite of designer tools that help integrate the designer and developer's workflows.
Expression Web was released earlier this month. It's a professional design tool for creating modern, data-driven, standards-compliant websites, and although it's targeted at designers, it has deep ASP.NET 2.0 support. You can find out more here.
Expression Blend (nee Expression Interactive Designer)
Designers building applications for .NET 3.0's Windows Presentation Foundation have used the pre-release version of Expression Interactive Designer (EID) to build rich user experiences. EID underwent a metamorphosis into the stylish Expression Blend, which sports a completely revamped user interface and significant new functionality.
Because Expression Blend and Visual Studio 2005 can both open .NET 3.0 projects, Expression Blend offers a great solution for allowing designers to work with a rich set of design tools to produce your XAML markup. Check Beta 1 out at the above link.