XnaControl is a wrapper that encapsulates the bits and pieces you need to create an XNA control inside a WinForms project. It's a self-contained project with no external dependencies except for MSBuild, XNA, and .NET 4. It is based on the XNA WinFormsGraphicsSample[1].
Using it is pretty simple: subclass XnaControlBase in your own project and implement Initialize() and Draw(). While the convention (as per the original XNA sample this is derived from) is to do your content loading in the Initialize method, I generally use this in conjunction with a tool that rebuilds XNA content files (http://github.com/eropple/XnaContent) when the content files change so I tend to do most of my loading on the fly.
-Ed Ropple (ed+xnacontrol@edropple.com)
[1] - http://xbox.create.msdn.com/en-US/education/catalog/sample/winforms_series_1