Graywolf dropped a list of essential WordPress plugins a while back entitled “SEO Plugins for WordPress”. Although a bit misleading, the article covers a variety of useful SEO plugins (some more so than others) that will do everything but tie your shoe. More recently, John Chow referenced an out of the box SEO solution which should also help you achieve better search engine results.
Meanwhile, I tend to fallback on the same WordPress plugins for all my optimization needs. In order from top to bottom, or rather header to footer, here they are:
SEO Title Tag – Super easy installation and highly configurable. Allows you to override page or post title tags with a custom ones.
Head META Description – Upload and activate. Simple. Done.
FeedSmith Plugin – Trick out your feed with all sorts of options including PingShot, a quick notification service that enables your feed to be updated in the widest variety of places as quickly as you add new content.
Google Sitemap Generator – Get a search engine compliant sitemap in seconds.
Common sense would also suggest you contain your core keywords in the post title since most WordPress themes typically wrap them in h1 or h2 tags. Furthermore, for maximum SEO impact, I recommend you read the definitive guide to semantic web markup for blogs.