youtubeplugin by jon is a simple TiddlyWiki plugin for embedding YouTube videos in tiddlers. It uses Google's SWFObject library to do the heavy lifting and exposes a nice simple API that currently looks like this:
* url: <string> * autoplay: <yes>|<no> * start: <integer> (number of seconds) * onEnd: <tiddler name> to open on end * onPause: <tiddler name> to open on pause