Jamie Rodriguez has published the 3rd version of Xaml Guidelines.

The goals of this paper are:
· To share an empirical reference for those just starting.
· To encourage others to share their practices and challenge the suggestions herein. These guidelines are not comprehensive—let us know what I missed.

It's a relatively small document but it contains a lot of information about:

• Overall Project Organization
• Naming conventions
• Styles and Template Guidelines
• Theming/Skinning an application

The guidelines are pretty sound and offer good starting point for developing a standards-document for your own company.