Many people know how much functionality can be expanded and externally changed using "monkey" scripts for services such as Gmail or Flickr. Today it's YouTube's turn.
1. YouTube Resizer
Earlier we talked about how to stretch a video on YouTube. This script is better for only one reason – it increases the size of the image without redirecting the user to another page.
2. YouTube Prevent Autoplay
Disables auto-loading of the video when entering any YouTube page.
3. YouTube BetterTitles
Many pages of the service have the same titles “YouTube — Broadcast Yourself". If you have several tabs with videos open, it's easy to get confused. This script allows you to change the headers of the most frequently used pages (for example, “Manage contacts” or “Most Recent (page 3)”.
4. YouTube Better Embed
The fact is that the embed code is incompatible with XHTML 1.0. If you still need to use the code, then this script will be useful to you.
5. YouTube Comments Next to Videos
Allows you to put comments next to the video to add them right while watching. This script was developed under the impression of the design of Google Video. If you want YouTube to look similar to Google Video, then use the YouTube Googler script.
via Five More Useful Greasemonkey Scripts for YouTube