If you're into financial blogs, this is a popular new plug-in: http://wordpress.org/extend/plugins/live-daily-stock-market-sidebar-widget/ Also, Aweber just created a new plug-in for WordPress users to generate sign-up forms faster...if time management is important to you.
i think i frequently use akismet, all in one SEO and few others. These plugins i frequently use: http://corpocrat.com/2008/10/04/10-best-wordpress-plugins-you-never-want-to-miss/