This is a list of the plugins that I use in my WordPress blogs and sites. External links open in a new window (tab) but all have the same target so you will not get loads of them.
Akismet is my basic spam protection.
The TrackBack Validator performs a simple but very effective test on all TrackBacks in order to stop spam.
WP-SpamFree is an extremely powerful anti-spam plugin for WordPress that virtually eliminates comment spam, including trackback and pingback spam. This plugin helped me stop a comment spam attack on one of my blogs.
Not used anymore
I used Bad Behavior for a while, up until it blocked me from logging into my own blogs. Needless to say that was the end of it and I removed the plugin.
SEO and being seen
I use Sociable for social bookmarking. The plugin adds social media buttons to your posts, you can pick which buttons you want plus where they shall be shown. I only show them on single post pages.
Google (XML) Sitemaps Generator for WordPress makes things easier for search engines.
Homepage Excerpts gives you options concering how many full posts to show and where. Read more on the plugin page.
WordPress.com Stats is a really nice plugin. It is Automattic’s stats system which focus on just the most popular metrics and provides the information in the dashboard..
Not used anymore
StatPress is an excellent tool that gives you statistics in your dashboard but it also logs a lot in your database. That is the reason I dropped this plugin.
Click Tags makes tagging posts a lot easier.
I use the Random Posts Widget to bring older posts back into the light.
Tag Functions lists tags in the same way you can list categories. It also adds a sidebar widget making it easy to add a tag list to a widget-enabled theme. See this plugin in action in the left side menu.
Quotes Collection is great for using random quotes at your blog.
Ajax Edit Comments allows users and admins to edit comments on a post. Users can edit their own comments for a limited time, while admins can edit all comments.
CommentLuv creates a titled link to the commenters last blog post.
Subscribe to Comments enables commenters to sign up for e-mail notification of subsequent entries.
Comment Relish makes it easy sending a short ‘thank you’ message to users when they first comment on your weblog.
Comment Timeout closes comments on old posts on your blog. In the options you decide how long commenting shall be possible.
Using WordPress as CMS
Using Page Category Plus makes it possible to assign categories to pages. The plugin uses the same categories you use for ‘Posts’ and, in effect, treats Pages as if they were Posts. Read more in Using WordPress as a business directory.
I have installed WordPress Mobile Edition. This plugin shows an interface designed for a mobile device when visitors come to your site on a mobile device. Mobile browsers are automatically detected, there is no configuration needed. Installing is easy, just a plugin plus a special theme.
404 Notifier logs 404 hits and will notify you of them via e-mail or in an RSS feed.
The WordPress Database Backup creates backups of your core WordPress tables as well as other tables of your choice in the same database. You can have the backups stored at your server or emailed to you.
I use Dagon Design Secure Form Mailer Plugin For WordPress for my contact forms.
FeedBurner FeedSmith plugin handles my feeds from FeedBurner.
You can comment at My WordPress plugins which is my post about this page.