Doktype external as typolink
When you want to have a page in menu which is a straight link to a file (like pdf) you have to create a page type external url and create the link manually. There is an extension (from2007) jb_external_typolink that includes the element/filebrowser to the link field. This way you can easily add a file, external url or email link as a menu item.
Improves greatly the usability and I think it would rather be a core feature than an extension.