It is available on my machine running Mail in Snow Leopard, but only in the header for a New Message window -
You may need to drag the window wider to the right in order to have that pop into view. If it still doesn't show, check the items set for view in the toolbar: with the New Message window active, select "Customize Toolbar..." from the View menu, and add that item if necessary.
Note - you can create your own stationary very easily. Make any changes you want to a message in the New Message window, such as background color, font and styling, text blurb, etc.; then select "Save as Stationary..." from the File menu. Give it a handy name when asked.
Once you do that, it will be available in the "Show Stationary" pulldown menu.
Thank you Don, once I opened a new message I saw the templates. I was, stupidly LOL, looking at the main mail page and did not see it. But when I read your message, the light switch came on, that of course I won't see it until I'm in the message window. Thanks for the kind how to, I needed it today ;-)