Adam Nathan, the one who brought us the excellent pinvoke.net Wiki, had released an addin for Visual Studio that integrates the pinvoke.net site and allows you to insert DllImports for API declares right into your code. I read about this a few days ago and I just tried it today. Really cool stuff. You can both insert DllImports into your code, or submit DllImports to the Wiki, all from within VS. Take a look.
Take a look at Adam's post on his blog for more details and screenshots, or download the addin from the workspace on GotDotNet. Awesome work Adam! Thanks a ton.