Here is a list of five WordPress plugins that allows easy conversion of posts to pages, pages to posts or posts to custom post types etc in bulk or one by one.
pTypeConverter
Easy interface post type converter plugin that converts post types from one to another. You can filter posts by title, type, author, date and convert a few or all at once. Its role capability prevents unwanted users from converting content.
Convert Post Types
Bulk conversion plugin converts many posts or pages to a custom post type or vice versa. You easily limit the conversion to posts by category and child pages. New taxonomy terms can also be assigned which will be added to the posts’ existing terms.
Post Type Switcher
This plugin adds drop down option for selecting post type from post edit page and quick edit option. You can choose combinations from post to page, page to post, post to attachment, post to custom post type etc etc.
Post Type Convertr
Converts lost of posts to custom post type or vice versa using the list of registered post types. Also using this plugin you can convert from one taxonomy to another and the lists are populated just as that of post types.
Vice Versa
Another WordPress plugin for converting Posts to Pages and Pages to Posts.