After reading this question about meta keywords, I've been wondering : of all meta tags, which ones are really worth the effort ?I know that the description is used in google search results, and the content type and encoding are used by the browser, but what are the other tags that we should always include in our pages ?
Which meta tags are not worth the effort?
html;meta tags
Meta tags are used for many different purposes (such as Dublin Core, ICBM, Open Graph Protocol, Powder) and generally have some  specific uses that are important to some sites.For SEO purposes and usability, you don't really need any metadata other than title, content-type, and description in your head section.As general advice, only implement a meta tag if you have a specific reason for doing so.  Want a Facebook Like button? Great, implement the Open Graph meta tags!  Don't like how Google caches your pages?  Add a Googlebot noarchive tag.  If you go ahead and implement tags without a clear understanding of why you are doing so, you are  increasing the size (and decreasing the performance) of your page without benefit, and increasing the risk of getting caught flat-footed if the tag causes an unexpected side-effect.There are many sites out there that list meta tag recommendations (here's one example) but these are generally not comprehensive and become less and less valuable over time as the web changes.