WordPress.org

This plugin let's you add a gallery of YouTube-videos to your site, displaying thumbnails for each video. With Shadowbox JS, Fancybox for WordPress or Thickbox installed you can chose to open videos in a box on your site, rather than going to YouTube.com

To add a YouTube SimpleGallery to a Post or Page, simply use the following code:

[youtubegallery]
Avatar Trailer HD|http://www.youtube.com/watch?v=cRdxXPV9GNQ
Call of Duty Modern Warfare: Deathmatch|http://www.youtube.com/watch?v=xqTac_O_wh4
The Fast Show: Unlucky Alf|http://www.youtube.com/watch?v=jJK-G9-dLzw
Jozin z bazin|http://www.youtube.com/watch?v=S4aqM_wu6Ns
[/youtubegallery] 

The titles/description is optional; add them before the links and separate with | (pipe).

To use with Widget(s), add a YouTube SimpleGallery widget to your sidebar, and put URIs (with optional titles) in the textarea.

Note that each YouTube must be separated with a linebreak, also in widgets.