Facebook makes your site deeply social by integrating functionality from Facebook.
Bad Behavior complements other link spam solutions by acting as a gatekeeper, preventing spammers from ever delivering their junk, and in many cases, from ever reading your site in the first place.
Share Buttons by Lockerz / AddToAny helps people share, bookmark, and email your posts & pages using any service, such as Facebook, Twitter, Google, StumbleUpon, Digg and many more.
StatComm provides realtime statistics on your blog, collecting information about visitors, spiders, search keywords, feeds, browsers, OS and more.
Theme-Check allows you to run checks on the current theme before uploading to WordPress. This plugin uses the same API and is kept more or less in sync with the WordPress.org uploader tool.