Userscripts.org

Removes ads and unwanted sections (configurable), allows downloading and resizing videos, changes the default video quality, expands the description and the video size, can prevent autoplay and autobuffering, etc...

Download Link + Quality Selector + Rollover Preview + Media Controller + Media Resizer + More...

Turn the lights out for easier watching of YouTube videos!

Removes ads and unwanted sections (configurable), allows downloading and resizing videos, changes the default video quality, expands the description and the video size, can prevent autoplay and autobuffering, etc...

Adds video titles, shows previews and embeds on click. Also supported: Vimeo, LiveLeak, WorldStarHipHop, Nicovideo

Gets the old order of subscriptions on the YouTube start page back.

Removes ads and unwanted sections (configurable), allows downloading and resizing videos, changes the default video quality, expands the description and the video size, can prevent autoplay and autobuffering, etc...

Make YouTube more like Google Video

Adds a download button to every video on YouTube. Multilingual, Auto-Update & Multiformat supported! (Flv + high-quality Flv & Mp4!)

Automatically Scale YouTube ect.. to Largest Possible Size & HQ/HD Quality Video. Scroll down to read comments without missing video, more...

Take youtube back, force it to search for worldwide contents! Also forces youtube to use secure SSL https:// pages.

Multiple Video Sizes with realtime switching supported, along with 3 different bandwidth modes! Unavailable video checking, LiveLeak support, version checking, inline embedding. YouTube's URL format means you click videos blindly. This appends ...

Enabling the lights out feature on YouTube for every video.

Inlines video player for links to: Youtube.com , Vimeo.com and Twitvid.com at the every website on the net. Позволяет просматривать видео прямо на сайте, где установлена ссылка на видео. не уходя на youtube/vimeo... А теперь ещё добавляет превь...

Detaches video and places it in a movable window.

This hack will eliminate the need of Javascript for playing clips on YouTube site. (Handy if you have NoScript extension on)

Optimizes YouTube for bigger resolutions and gives you the opportunity to hide various sections of the video playback page, disable autoplay, enable HD and download videos. All this and more can be utilized through a built-in configuration menu:

Removes ads, allows downloading and resizing videos, displaying all comments on video page, etc.

Allows you to ask multiple sites for a download link using simple button interface. Sites include Youtube, Megavideo, Veoh and more.

Expands the full description of the youtube video being played by clicking 'more info' link on the top right panel on youtube, Showing you full description, category and tags.

Removes annoying Google+ pop-up from YouTube.

Creates a download link for youtube videos with different resolutions. Optionally removes comments on video pages. Multilingual.

Stitch together YouTube videos that are split across multiple parts.

Plays videos directly in pages with video hostings links // Проигрывает видео в сообщениях с ссылками на видео хостинги

Bypasses the YouTube Censor for anonymous users

Bypass YouTube's age verification requirement by playing age-restricted videos directly on the verification notice screen. ONLY allows watching, does not provide a comments page, etc.

Automatically redirects users from the what to watch tab, i.e. homepage, to the uploads only tab under subscriptions.

Bypass age verification (no account required), auto-clear viewing history, hide front-page feeds, show blocked comments

[OUTDATED]Allows you to switch the look of the homepage. **BROKEN AS OF DECEMBER 7, 2012 UPDATE TO YOUTUBE

Always play youtube videos in highest available quality, everywhere. Works with embedded videos too. Flash/HTML5.