Windows only: Standalone application Theme Builder creates themes for Microsoft Word documents, Excel spreadsheets, PowerPoint presentations and even Outlook emails — allowing you to create a consistent look and feel across all your documents.
Downloading the application requires using Microsoft's annoying File Transfer Manager, which usually requires Internet Explorer, and once you get past that hurdle you need to make sure that you've got the .NET Framework 3.0 and Office 2007 Interop installed — but once you've successfully navigated through all of those, the application is relatively easy to use.
You can make a copy of the themes under your Office Install -> Document Themes directory, and then open them up in the Theme Builder application to customise just about any aspect of the theme. Once you've finished, you can save them out to your documents folder and use them from any Office application by choosing the Browse option under the themes panel's drop-down menu. If you want them globally available, you can save them out to the Office installation directory where the rest of the theme files are.
The application is a bit of a pain to get going, but could be a huge timesaver for making sure all your Office documents have a consistent look. Theme Builder is a free download for Windows only.