I\'ve looked for tutorials on using HTML Agility Pack as it seems to do everything I want it to do but it seems that for such a powerful tool there is little noise about it
HtmlAgilityPack's HtmlDocument implements IXpathNavigable, thus it uses the standard .NET XPath engine. Any XPath 1.0 documentation will be applicable, especially if it talks about System.Xml.XPath.
"//comment()" finds all comments
"//meta" finds all "meta" elements
HtmlDocument was designed to look very much like XmlDocument, so examples and tutorials about it will be somewhat applicable.
Some MSDN links: