Userscripts.org

Buffers the video without autoplaying, removes in-video ads, and puts it in hd if the option is on

Adds FLV, MP4, 3GP, and 720p download links to YouTube.

Removes video advertisements

Adds the national flag icons next to each username in the comment section of Youtube.

Enhances your pirating experience by adding torrent links to iMDB, Rotten Tomatoes (and MovieFone, soon).

Stop Autoplaying Video On YouTube Profiles

Changes javascript links into direct links

Customize YouTube's Player Page

Several customizable options. Special support for Userscripts.org (new interface, fix for pre tags, and allows you to hide the install warning box and footer) Changes text fields, buttons, links, selects, and text areas.

Watch videos in high quality automatically. Now has a UserScript command to toggle a confirmation box. Made for people who don't login or save cookies. Uses JavaScript instead of &fmt=18; no reloading pages

Automatically "likes" videos from users you choose, or anybody.

Removes unnecessary parameters from links like feature=channel

Completely removes the annoying gray playlist at the bottom of YouTube. (In opposition to just hiding it.)

Automatically pauses the video when you switch to a different tab or window, and automatically plays when you come back to it

Adds extended functionality to the youtube player such as player refreshing if video stops loading, user specified seek ahead, stop video loading, and more

Gets right of the footer, copyright, google ads, big frontpage ad, side announcement box, "may not be suitable for minors" warning, and other annoyances.

Hide the videos you've already seen

Adds a button that redirects to KeepVid's YouTube download service for the video you are currently watching.

Creates links under embedded youtube videos and shows thumbnails when hovered over

Adds &fmt=18 to the url for high quality but not if any &fmt=x already exist and adds &fmt=18 to all the links

Skips the das captcha page on YouTube

Adds a "By Date" button next to the search button

Shows hidden thumbed-down comments that can't normally be seen

Well It Changes The Look of Animecrazy And Moves Some Links Just started this Project

Adds a menu under YouTube video with available MP3 files found on ZippyShare and Hulkshare.

Hides comments, preserves brain cells. Click headers to toggle.

Make the YouTube dislike bar red again.

Pauses the video when you click anywhere on it

Removes main youtube ads, does not remove in-video ads.

Adds &fmt=18 to all YouTube links