Universal Reference

This module solves the issue of referring to both external and internal content from within a node.

It creates a field type which may both refer to an external URL, if an http:// (or other allowed protocol) link is entered, or autocomplete on node titles, to refer to internal nodes by their node ID.

You can also specify a custom title or use the referenced node title or URL as default title.

This module more or less a combo of the link module and the node_reference module.