Akismet is a staple -- it helps get rid of spam. AddThis shows a button on each post that allows visitors to add the post on social bookmarking sites. Analytics plug-ins are also useful. Try Google Analytics for Wordpress. WP-PageNavi adds a more advanced paging navigation to the blog.
In my opinion Breadcrumbs is a top most popular WordPress plugin.This is one of those WordPress plugin that are based on obvious ideas. This adds the ease to the navigation system which will save a lot of your time.
i always use One Click Plugin Updater, WordPress.com Stats, WordPress Related Posts, Auto Social Poster, and All in One Adsense and YPN in all my blogs. I got they very useful for me.
For some reason, the one click plugin updaters do not work on my server. Must be a real crap server / limitations. I would definatley go for the advertisement plugins and HeadSpace
Why me blog has 404?I can not find that page,but yahoo spider could crawled it,i can not understand it? And i think the "all in on seo" and "Akismet" is great.