Ruven

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

Ruven Themes: Gallery

RT Gallery enables a "Gallery" post type and "Category" taxonomy.

ImportWP

JC Submenu plugin allows you to automatically populate your navigation menus with custom post_types, taxonomies, or child pages. An easy to use plugin created to be a lightweight menu extension.
Also output a selected section of your dynamic menu through our advanced submenu widget.

JC Submenu

JC Submenu plugin allows you to automatically populate your navigation menus with custom post_types, taxonomies, or child pages.

Ruven Themes: Gallery vs JC Submenu