This plugin can validate more deeper. Not only the HTML tag's attributes, but also the contents of attributes. You can set your own regular expression for attributes. For example, you want limit users to post Flash videos only from YouTube or Google, then you can restrain the src attribute.
Sample posts: This post shows you an embedded YouTube video and this has a image floating at right side.
Visit Plugin page or directly download HTMLTagAttributesValidator.php.
Any comments on this plugin are very welcome.