"Embedded files Plus" (repository_areafilesplus) plugin allows to re-use the files embedded in the current text area and provides a simple interface to delete unnecessary files.

This plugin is designed for Moodle version 2.3 and below since they don't have support for TinyMCE plugins.

For Moodle 2.4 and above it is recommended to use instead repository_areafiles and tinymce_managefiles.

To install: copy folder areafilesplus to /repository/, login as admin and run upgrade script.

To use: Open any form with textarea in HTML mode, insert an image using filepicker as usual. Click "insert/edit image" again and in filepicker window select repository "Embedded files". The list of all files used in this textarea will appear and user can re-use any of them. The link "Manage" on top can be used to delete unnecessary files.
Note that other windows need to be refreshed afterwards.
You can insert media and/or links to other files as well. Note that files in filepicker are always filtered by the accepted file types (for example when you add an image you will only see images even when other files present in area).

How to use Repository "Embedded files", TinyMCE plugin "Manage embedded files" and Repository "Embedded files plus":