One of the most common uses for menus is to link a static page, so it would be great to have on the edit menu item, a select field, so you can select a defined, content type. (published pages by default).

The path text field could be necessary anyways so a radio button for entering a path should be a second option in a 2 radio button list.

(o) Content [ About us ][v]

( ) Path

Ps. Also listing the aliases on the select field could be an option....