Facebook allows you to define custom objects within an app. Then you need to add a og:type metatag with the content "[namespace]:[custom_name]".

It would be really helpful having a way to add a custom type.

Also you can define extra properties on your objects that you need to define in your page as a metatag like <meta property="[namesace]:[property_name]" content="[property_contents]" />. It would be great to add support to properties like these per node type.