Microsoft has released Visual Studio 2010 SharePoint Power tools today on the Visual Studio Gallery. These tools will extend the Visual Studio 2010 with sandboxed-compatible visual web parts and compile time errors for the disallowed code in the sandboxed solution.

 http://visualstudiogallery.msdn.microsoft.com/en-us/8e602a8c-6714-4549-9e95-f3700344b0d9

This is must for any SharePoint developers and make sure your development machine has these tools installed.