This modification to zen cart will allow you to set up a reciprocal links directory that is editable within your zen cart admin area.  It allows you to set up as many link categories that you want and also allows for banner links as well as text links.

This open source mod has been written for 1.3.9, 1.5.0, 1.5.1, 1.5.3, 1.5.4, 1.5.5