Khanh

(Beta) An extension of Fields, a custom field management plugin. PostLinks provides additional field types such as Series, PhotoLink and PostLink.
Three new field types:
<ul>
<li>PostSeries: link your posts into series and display them with the [series] shortcode, also it comes with 2 widgets</li>
<li>PhotoLink: to be added</li>
<li>PostLink: to be added</li>
</ul>

PostLinks

(Beta) An extension of Fields, a custom field management plugin. PostLinks provides additional field types such as Series, PhotoLink and PostLink.

pixelgrade

George Olaru

Andrei Lupu

With <a href="https://github.com/pixelgrade/pixfields" rel="nofollow ugc">PixFields</a> you can have a custom fields visual manager.
Note: this plugin does not add any style to the output of custom fields. Its just adding metadata and offers a way to overwrite the html from the theme. 
The theme should style the output of the metadata.

PixFields

PixFields offers you a nice interface to add custom metadata into your favorite post type.

PostLinks vs PixFields