Link

The LINK module provides a standard custom content field for links. With this module, links can easily be added to any type of content and any profile, and include advanced validation and different ways of storing internal or external links and URLs. It also supports an additional link text title, site-wide tokens for titles and title attributes, target attributes, CSS class assignment, static repeatable values, input conversion, and more.

Requirements / dependencies:
Drupal 6: CCK Module
Drupal 7: Fields API is already in core
Drupal 8: The Link module is included in D8 core. However, remember to enable it. It is disabled by default.