You can look it up from the admin panel. Mouseover the post links and you'll see the ID's.
Another option is to modify the template slightly and put the post ID in a HTML comment (for example <!-- ID -->) so you can view it from the source. You can see the ID tag and how to call it in your templates here:
http://codex.wordpress.org/Template_Tags/get_posts
You could even make it so only logged in admins could see it.