I'm happy to announce that the PInvoke Interop Assistant tool is now available on CodePlex. This includes the binaries, source code and the dev authored unit tests.
It is hosted on the more general CLR Interop Tools page.
I will be actively maintaining this tool in the future and (hopefully) adding more features. There were several features we cut just before release due to QA costing that I would like to add back (including VS integration, wrapper functions).
Please post any suggestions you have for the tool on the site and we will definitely consider them.