Codeko

With this plugin you can set any post type (or posts types) as parent of any post type.
Urls will be wellformed, redirects will work, breadcrumbs will work fine.
This plugin is recomended when you need a url structure with a mix of post types. Any url structure you can imagine could be done.
Post types rewrite slugs will be ignored

Custom Posts Parents

Set any post type (or types) as parent of any post type. Any post structure can be created with this plugin.

James Irving-Swift

Electric Studio

Adds a filter in your wp-admin that allows you to choose a parent page so that only the children of that page will be shown. Very useful if you have a lot of pages! 
Thank you to Brian Krogsgard for the changes in version 1.3 (Twitter: @Krogsgard)

Filter Pages by parent in admin

Filter pages in the wp-admin by their parent pages

Custom Posts Parents vs Filter Pages by parent in admin