Codeplex has lots of interesting tools. Here is one I stumbled on today - This is a much easier way of making Office 2007 themes and styles than manually doing it through the Word or PowerPoint interface:

The Open XML Theme Builder is a tool that helps with the creation of theme files (*.thmx) that encapsulate the visual appearance and formatting of a document in order to help create a better looking document. Theme files can be used by Microsoft® Office PowerPoint® 2007, Microsoft® Office Excel® 2007, and Microsoft® Office Word 2007.

Open XML Theme Builder - Home