Ruven

This plugin registers a custom post type for portfolio items and a taxonomy for portfolio types.
Selected themes by Ruven provide templates to display portfolio items. 
In other themes you most likely have to add them by yourself.

Ruven Themes: Portfolio

RT Portfolio enables a "Portfolio" post type and "Type" taxonomy.

swergroup

This plugin let plugin and theme authors to display their work in their main WordPress. It provides some helpers:
<ul>
<li>two custom post types: plugins and themes</li>
<li>SEO-friendly URLs</li>
<li>fetch (and cache in transient) plugin/theme info from the latest readme.txt file</li>
<li>fetch (and cache in transient) rating / support / downloads info</li>
<li>plugin info from readme file as custom post metadata</li>
</ul>
Planned in the next release:
<ul>
<li>widgets with plugin info</li>
<li>shortcodes</li>
</ul>

Developer Showcase

Plugin/theme showcase plugin for WordPress plugin/theme authors and developers.

Ruven Themes: Portfolio vs Developer Showcase