must have wordpress plugins

WPDB Profiling
a great tool to check out your wordpress theme’s performance, it shows number of db requests and timing below the footer when logged in
All in One SEO Pack – “home description” on the settings page gives you the google excerpt (or add meta description to header, same thing, but the plugin is more flexible and allows you to overwrite settings per page/post)
caching can greatly improve your site’s performance, however, it depends on your hosting and results may differ
for my blog/hosting DB Cache Reloaded Fix in combination with WP Avoid Slow works best
W3 Total Cache (many options to configure, my server choked)
WP Super Cache (I’d still consider it the best tool, but it really depends on the web server)
google xml sitemaps
submits a sitemap to all major search engines