The Node Relationships module provides methods to complete two way relationships between content types enhancing the features of node reference fields.

It provides the following features:

• Enhancements for node reference fields: "Search and reference view" (single and multiple selection based on dynamically configured views) and "Add and reference". This feature uses the Modal Frame API to provide a popup dialogs from buttons attached to node reference fields configured to use the autocomplete widget.
• Automatic back references using dynamically configured views that are able to extract the relations from existing database information. This views can be rendered using a myriad of methods in the node view.
• The Node Relationships module provides default views for each feature that can be modified and/or cloned (recommended) should you need to add more fields, filters or change any other option to suit your needs.
• Basic entity relations diagram (ERD) that can be used to view the relations of each individual content type. The provided diagram can be used to walk the relationships of all types in the system.

More information in the project page.