here is the thing: what do you summarize as meta tags, do you only mean meta tags or everything in the
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.
(not really a meta tag, but in the
section) because google uses it (in most cases) as the headline of the listing in the SERP
a very efficient directive to control the indexing behavior (and to some extend the crawling behavior and value allocation) of google
get rid of snippets that use http://www.dmoz.org/ for descriptions
advises google to not index the images found on this page (but they might get indexed if they are used on other pages)
(not meta, but in the head) communicate a canonical URL (the one you would like to get indexed) to the search engines.
together with the canonical a cool way to communicate alternate language versions of a page to google
if you want to achieve rich snippets in google by using microformats, these meta informations are necessary.
indication of content type and encoding
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)