User-agent: *
Disallow: */trackback*
Disallow: /wp-*
Disallow: */feed*
User-Agent: MediaPartners-Google
Allow: /

I’m no expert (I didn’t write it myself), but I believe you should add the last two lines if you use Adsense on any of the blocked pages. Otherwise you’re blocking the Adsense bot as well as the search bot and won’t get ads in context.

Also, note the /wp-* line. This should block everything that starts with wp, including the files (such wp-admin.php) and the folders (such as wp-include), etc. I can’t see any reason to include anything that starts with wp (unless you have a wp tag or category).

I don’t use tags yet and I leave blocking category and archive pages (I know you don’t want to block this) to the All In One SEO plugin. It adds noindex,follow to the html on the page itself rather than using robots.txt.

As I say, I’m no expert on this, but I thought I’d share my setup.