Here is the most comprehensive list of all the Wordpress plugins you need as of today to maximize the potential of your own blog. For months, I’ve been able to bookmark hundreds of plugins, and now I’ve done all the work for you by sorting the best plugins you only need to truely leverage Wordpress! In no particular order, here they are!
IntenseDebate http://intensedebate.com/ Replaces default comment system with advanced commenting, threaded replies, karma points (not for individual comments), Gravatars, RSS, ability to reply to comments from email (great to reply from your Blackberry), all in one management from the website for users. It also comes with the optional Intense Debate Top Commentators sidebar widget to display your top commentators, great to encourage commenting (however, the Disqus one below is a lot more comprehensive).
Disqus Commenting System http://disqus.com Replaces your comment template with the more advanced Disqus comment system. Disqus is also the only system to support Facebook Connect out of the box. I’ve contacted IntenseDebate directly and they told me there is no current plan to support Facebook Connect. Disqus also features RSS, Gravatars, threaded comments, comment karma, and lets you easily see comments made by the same user on other sites. I prefer Disqus as it offers Facebook Connect support out-of-the-box that could help you tap into the Facebook community. Disqus also features top commentators, recent comments widgets. Also, with Disqus you can enable video comments with seesmic.
Digg Digg http://www.mkyong.com/blog/digg-digg-wordpress-plugin/ Adds Digg, Reddit, Yahoo Buzz buttons with counters for your readers to easily vote for your posts from your page. I was able to contact the author who also told me Stumble Upon support is on its way as well.
Sociable http://wordpress.org/extend/plugins/sociable/ Automatically add links to your favorite social bookmarking sites on your posts, pages and in your RSS feed. You can choose from 99 different social bookmarking sites including Digg, Reddit, SU, Mixx, Propeller. You can also add e-mail and print buttons. It also supports TwitThis, but the plugin can be made easier by using TinyURL (or another URL shortening service) and automatically logging the user into Twitter with the URL and Title already shown.
Lifestream http://wordpress.org/extend/plugins/lifestream/ Lifestream displays your social feeds and activity from many social sites. Includes support to display your Flickr photos, Facebook feed, Friendster feed, Youtube videos, Twitter updates, any other RSS feed, from your other blogs, etc.
WP Greet Box http://wordpress.org/extend/plugins/wp-greet-box/ Displays different greeting message to your new visitors depending on their referrer URL. For example, when a Digg user clicks through from Digg, they will see a message reminding them to digg your post if they like it. The plug-in also includes out of the box support for getting messages from users coming from Reddit, SU, Facebook, Google (shows searched keywords as well), Mixx, etc. You can also easily add your own custom greeting from people coming from any site you choose.
WP-SpamFree http://wordpress.org/extend/plugins/wp-spamfree/ An extremely powerful anti-spam plugin for WordPress that virtually eliminates comment spam, including trackback and pingback spam. I find the plug-in works surprisingly well by eliminating all automated spam. It does somewhat use a bit of bandwidth sometimes.
WP Super Cache http://wordpress.org/extend/plugins/wp-super-cache/ This plugin generates static html files from your dynamic WordPress blog. After a html file is generated your webserver will serve that file instead of processing the comparatively heavier and more expensive WordPress PHP scripts. Some people have complained about compatibility problems with other plugins, so exercise some caution here and follow the instructions carefully. However, the plugin is very good and can save you a significan amount of bandwidth.
Popularity Contest http://alexking.org/projects/wordpress Shows your readers your most popular posts based on views, comments, pingbacks, among other criteria. You can also change the weight of each criteria to determine the most popular post.
WP Since Last Visit http://alexking.org/projects/wordpress Indicates with a small “New” picture beside your post to users who have not yet seen your post from their last visit. Also works with comments.
Video widget http://www.nikohk.com/plugin-wordpress-video-widget/ Easily display videos from many different video sharing websites on your sidebar or blog, including from YouTube, DailyMotion, Google Video, Metacafe, Reever, MySpace, Blip.tv, Quicktime, Windows Media Player, among many others
FlickrRSS http://eightface.com/wordpress/flickrrss/ Lets you easily display your Flickr photos on your blog, comes with a sidebar widget. Note: Lifestream plug-in also supports this so you may not need this plugin.
Facebook Connect Community http://www.sociable.es/facebook-connect Allows your users to sign in with their Facebook account. It also supports comments to be sent to the users news feed, which can draw you some good viral traffic. However, it does not work with IntenseDebate. I just contacted IntenseDebate and they told me they do not plan to offer Facebook Connect support, which is unfortunate because that would make life a lot more easier, especially for people who want all the advanced features of IntenseDebate but also want the ability for comments to be sent to the Facebook newsfeed.