Arunas Liuiza

This plugin enables users to easily note the source of republished text. It adds a custom post type ‘Sources’ and a metabox to choose from various sources in post editing window.
ATTENTION: This is still an early development version (aka ALPHA), thus use with your own risk. It has the basic functionality, but not many configuration options and some bugs are probably present.
Basic functions:
<ul>
<li>Allows to create list of possible sources using Custom Post Types functionality;</li>
<li>Creates a meta-box in post editor screen to choose from list of available sources;</li>
<li>Customizable template – you can use your own html and shorttags %title%, %title_attr%, %text%, %img%, %img_h%, %img_w% and %link%;</li>
<li>You can use template tag <code><?php tinysource_show(); ?></code> to insert plugin output;</li>
</ul>
TO DO:
<ul>
<li>More customization options</li>
<li>Automatic insertion after post text</li>
<li>Localization</li>
</ul>

tinySource

This plugin enables users to easily note the source of republished text. EARLY DEVELOPMENT VERSION. DO NOT USE IN PRODUCTION ENVIRONMENT.

Nilambar Sharma

<h3>Source Affix</h3>
This is right plugin for you if you want to add source link to your post. It adds separate meta box for the input of source text. You can use this feature to any Post or Page. Even more, it also supports custom post type. Several plugin settings are also available. You can show sources in comma separated form or in an unordered list. You can append or prepend source to the content.

Source Affix

A plugin for adding source links to your Post. Supports Page and Custom Post Type also.

tinySource vs Source Affix