Better Delete Revision allows you to remove old post revisions and related meta content and optimize the database.
GTS Translation provides high quality human translation of your blog content using community translation (crowdsourcing).
IE9 Pinned Site adds support for Internet Explorer 9′s pinned site features to your WordPress blog.
AddToAny: Share/Bookmark/Email Button helps people share, bookmark, and email your posts and pages using any service, such as Facebook, Twitter, Google Buzz, Digg, Delicious, and well over 100 more social bookmarking and sharing sites.
All in One Webmaster has options to add Google, Bing, Alexa, Blog Catalog, Yahoo’s Webmaster and Analytics code (meta tags).
FourSquare Integration allows you to display your last checkins as a list or on Google Map on pages and posts.
Simple Twitter Connect is a series of plugins that lets you add any sort of Twitter functionality you like to a WordPress blog.
YOURLS: WordPress To Twitter allows you to use YOURLS (a free GPL URL shortener service) or another public service (tinyURL…) to create short URLs of your posts and tweet them.