Easylinks

This module is intended to supply Drupal sites with an easy, non-intrusive mechanism for allowing visitors or registered users to suggest links to other sites.

You have the choice of having suggested links "auto-approved" i.e. approved without administrator intervention or (by default) look at the list of links and approve those that have been suggested.

There is also basic functionality for reporting broken links. And settings now include option to open links in new window.