If I were asked which WordPress plugins I would recommend to bloggers that use this popular platform, and want to enhance the usability component, I would list the following five:
1. Akismet [plugin’s site] by Matt Mullenweg – Checks comments posted in your blog against their own database and places suspicious ones into a Spam folder. It does a great job, filtering all of the spam in your blog (hence, making it look much cleaner that it would’ve looked without this plugin), as well as makes your job of comment moderation much easier. Keep in mind though that occasionally (as often is the case with email spam filters too) a totally kosher comment may land in that Spam folder. So you want to look through the comments stored in this folder every once in a while (to whitelist the good readers).
2. Subscribe To Comments [plugin’s site] by Mark Jaquith – Adds a check box that a commenting reader may tick if they want to be notified of replies to their comment(s). A must have if you want to really engage your audience, which is important not only for your blog’s popularity to grow, but also because some of the most important thoughts and conclusions are born in discussions.
3. WordPress Popular Posts [plugin’s site] by Héctor Cabrera – Excellent plugin that sorts your previous blog posts by popularity. Popularity is defined by you. It can either mean “most comments” or “most views”. Regardless of the determinant that you choose, each post can still show both the number of views, and the number of comments (it is all easily customizable). I chose to use this plugin in combination with the Most Popular Posts plugin (which ranks posts by the number of comments one), and have one display posts in order of most views (giving a “Most Viewed Posts” header to this ranking), and the other – by most comments.
4. SexyBookmarks [plugin’s site] by Josh Jones and Norman Yung – One really sexy plugin that allows for an array of social bookmarking options to be placed under each of your posts. See it in action right under this post.
5. Seesmic WordPress [plugin’s site] by Seesmic Inc – Great plugin for adding video comments (recording them right within your own blog using Seesmic’s platform). Truly adds a new dimension of online communication and brings a blog alive. Even if your readers never use it, use it yourself!
I have arranged the above plugins in order of priority (you can live without video comments, but can’t without filtering those spam comments effectively). I use all of the above.
If I haven’t listed a plugin that in your opinion can greatly improve a WordPress blog’s usability, and enhance user engagement, please write about it in the comments area below. I am open to suggestions, ideas, and always eager to learn from the experience of others.