Evan Solomon

<a href="http://oembed.com/" rel="nofollow ugc">oEmbed</a> is an easy way to embed media. It turns links into embedded content automatically. WordPress has supported it in posts for a while, but not in comments. This plugin uses the oEmbed support already in WordPress and adds it to comments.

oEmbed in Comments

still works

WordPress supports oEmbed, but only in post content. This adds oEmbed support to comments.

johnh10

No need to search YouTube and copy/paste videos into WordPress. Video Blogster 
Lite will automatically fetch the title, description, thumbnail, and 
statistics for each video in your keyphrase search. Integrates seamlessly with 
WP-PostRatings and WP-PostViews.

Video Blogster Lite

Create a video blog in minutes! This plugin searches YouTube for content and automatically creates posts from the results.

oEmbed in Comments vs Video Blogster Lite