During the Windows Phone UI and Design Language session at Mix, the presenters talked about the Metro styled icons, and how applications of similar type should make use of the standard set of icons if possible. I had been hoping these icons would be released with the SDK, but I couldn't find them anywhere. It never struck me to just take them out of the powerpoint deck posted online (thanks for the suggestion Josh).
The image above is taken directly from the posted powerpoint file. Keep in mind that the icons you use in the ApplicationBar should not include the circle, and should be 48x48. So, if you want one of these icons just edit the above image in your favorite image editor and copy out the icon you want, remove the border, size it properly for 48x48, and remove the black background so that it is white foreground on transparent background.
Update: More official icons have been released on the Windows Phone Developer Blog.