Want to get started playing around with WPF applications, but you'd rather save your cash for some SLI video cards? Never fear - we've assembled a list of free (as in gratis) tools for most facets of WPF development.
Essentials
Visual Studio Express Editions (C#/VB.NET) and Visual Studio Extensions for .NET 3.0 will get you up and running and building "hello world".
Optional - Development
Microsoft Windows Software Development Kit for Windows Vista and .NET Framework 3.0 Runtime Components - this SDK includes a number of samples, tools and documentation that can be very helpful when developing WPF applications.
Optional - Design
Inkscape is an open-source vector graphics editor. It is ideal for creating vector icons, complex paths, geometries and the like. It's native file format is SVG, an XML dialect for representing vector graphics. In order to incorporate Inkscape into your WPF tool-chain you'll need this handy SVG to XAML converter, written by Andrej Benedik from wpf-graphics.com.
Optional - 3D
Blender is the free open source 3D content creation suite. You can use it to develop 3D content, which you then export to XAML using this export script from Daniel Lehenbauer from the WPF 3D team at MS. Note - the latest release of Blender seems to have some issues running on Vista. Also, to run the export script you will need to install Python.
Optional - Components
Xceed DataGrid for WPF is a free, commercial-quality data grid offered by Xceed. WPF does not include a datagrid as one of the build-in controls, and Xceed has more than filled this gap with their grid. You can also catch an interview with Pascal Bourque, one of the senior developers from Xceed on Channel9, talking about the new approaches and opportunities for developing components for WPF.