here is the thing: what do you summarize as meta tags, do you only mean meta tags or everything in the
<head>
of your HTML? the sloppy definition of meta tags mostly includes these elements as well.
these "meta" tags are still very very important for efficient SEO.
<title></title>
(not really a meta tag, but in the <head>
section) because google uses it (in most cases) as the headline of the listing in the SERP
<meta rel="description" content="because google uses this text here as the snippet text of the SERP (in most cases)
listing">
<meta content='noindex, nofollow, noarchive, nosnippet' name='robots'/>
a very efficient directive to control the indexing behavior (and to some extend the crawling behavior and value allocation) of google
<meta name=”robots” content=”noodp”>
get rid of snippets that use http://www.dmoz.org/ for descriptions
<meta name="robots" content="noimageindex">
advises google to not index the images found on this page (but they might get indexed if they are used on other pages)
<link href='http://www.example.com/en/vienna/cha-no-ma' rel='canonical' />
(not meta, but in the head) communicate a canonical URL (the one you would like to get indexed) to the search engines.
<link href="http://www.example.com/en/vienna/b/billa" hreflang="en" rel="alternate" />
together with the canonical a cool way to communicate alternate language versions of a page to google
<link href='http://microformats.org/profile/hcard' rel='profile' />
if you want to achieve rich snippets in google by using microformats, these meta informations are necessary.
<META http-equiv="Content-Type" CONTENT="text/html; charset=iso-8859-1">
indication of content type and encoding
<META NAME="google-site-verification" CONTENT="+nxGUDJ4QpAZ5l9Bsjdi102tLVC21AIh5d1Nl23908vVuFHs34="/>
a way to verify your site for google webmaster tools
stuff that is not important:
meta keyword tag, just forget about it. its useless (and if you put spammy words in it even of negative value)