Anyone who has their own Google Sites page may want to verify it for Google Webmaster Tools. At this time, unfortunately, it's not possible. Google Sites does not allow you to upload HTML files or add meta tags, so verification at this time seems to be something Google has not considered.
That said, the Google Sites team is now aware of the issue and Reid from Google has responded to the forums thread saying that they will be looking into it.
Forum discussion continues at Google Groups.