The October CTP is ready and will soon be posted. When Vista RTMs in November, the final rev of .NET Framework 3.0 will be released, and the final Fidalgo CTP with Cider will go out with it.
This will be the final release of Fidalgo, aka the "WinFX Tools for Visual Studio 2005." From here on out, you'll use the final Fidalgo CTP to build WPF applications on the retail platform. Here's the official story:
The Microsoft Visual Studio 2005 Extensions for.NET Framework 3.0 (Final CTP) provides developers with support for building .NET Framework 3.0 applications using the released version of Visual Studio 2005. These tools are provided as an early preview of technology being considered for the Orcas release of Visual Studio. This is the last release of this technology that will be in the form of a set of extensions for Visual Studio 2005. Any new technology in this space will be included in CTPs of the next full version of Visual Studio which is currently code named “Orcas”. The Visual Studio Orcas CTP releases will include some of the technology available in this CTP. The availability of this technology in Orcas will come online at various points during the development cycle and may have differences from features available by installing this product with Visual Studio 2005. You are strongly encouraged to install the Orcas CTP to get an early look at how these features will exist in the next supported version of Visual Studio.
So, the October CTP is the one to get, if you're doing WPF development into the future.