WUCO aka WP Ultimate Cleanup & Optimization, a free easy to use yet effective plugin designed to help you keep your MySQL database clean.
WP-Sweep allows you to clean up unused, orphaned and duplicated data in your WordPress. It also optimizes your database tables.
Deletes all unused tags, handy tool if you want to start over with a quick clean blog.
This plugin will help you to manage your upload folder, identify useless files and remove them and save space.
Clean up unused images and other files from your uploads folder.