Here is a quick list of the most common tags in a header and their SEO worth
title Very important. Don't leave your home page without it
meta name="description" Used for descriptions by directories and search engines, but no direct ranking value. Good to have, though.
meta name="keywords" Only used by some engines for inclusionary purposes only. Extremely limited use, and none for rankings.
meta name="copyright" No SEO value, good idea legally though
meta name="robots"Default behavior for an SE is "index,follow", so unless you want something different this is a waste of time. Can affect rankings by removing site from indexing. Can't add your site or force a visit though. The same applies to specific robots being mentioned, such as Googlebot.
meta http-equiv="pics-label" Only used for voluntary content ratings. No SE ranking value, but helps identify and exclude sites when a searcher uses Safe Search or similar.
meta http-equiv="expires" Not used by search engines unless expires=0, at which point they will not cache, as far as I know
The following are a waste of time and/or bad for you
meta equiv="refresh" Usually a bad idea - use a proper 301 instead.
meta name="distribution" Waste of time - intranet only
meta name="author" Ego purposes only outside of an intranet
meta name="generator" Not useful for search engines, is sometimes used by your web development tool (FrontPage is infamous for it)
meta name="revisit" No value at all. Does nothing.
meta name="vw.96" No value unless you own a Volkswagon, live in BC, and it's the years 1996-1998. Just dumb.
meta name="city" This Geotag, along with similar ones, are only used by Gigablast - no other use.
meta name="geo.region" Same as above, but not used by anyone major.
meta equiv="keywords" Using the http-equiv for things like keywords and description is a complete waste of time. Improper usage.
meta name="DC.title" Dublin Core only - no use for internet search engines. Same with DC.description
All Other Dublin Core tags: Same - no use outside of an intranet with a custom SE that uses them.
Here is an easy to use metatag and header generator, as well as more information.