Currently, I use:
Bad Behavior, to keep bandwidth wasting, email harvesting, and spam posting bots out of this site.
Permalink Redirect, to ensure that redirected permalinks (those entered without a trailing slash) return a 301 permanent redirect message.
Screw Nofollow, to disable the rel=nofollow attribute in the comments area.
Search Hilite, to highlight search terms when visiting from any popular search engine.
Search Pages, to allow pages to be searched as well as posts.
Spam Nuker, to manage spam deleted by WordPress' default anti-spam tools.
Translator, to present MacManX.com in 9 different languages (including English).
WP-ContactForm, to provide a contact form and hide my email address from spam bots.
I also use ShortStat (which is an external PHP script, not a WordPress plugin) to monitor live site statistics.