Developers need at least Visual Studio Professional Edition to create new domain specific language designers. These designers can be used by others who have at least Visual Studio Standard Edition.
The VISP Affiliate site lists other goodies in the VS 2005 SDK include "contents and samples for Team Foundation Server and Team Test extensibility, IronPython website and web project samples, 5 new Visual Studio PowerToys, managed parser & lexer generator tools (MPPG/MPLEX), updated documentation and many more IDE integration samples."
This release also includes a new version of the end user license agreement.