As you may know, WordPress is a powerful blogging, site building, and content management system. Because it's free and open source, there are literally thousands of ways to tweak, modify, and enhance it. Some of the best ways to build in additional functionality to the core WP installation is through the use of "plugins."

What are plugins and more importantly, which ones are best?

Plugins are files that you upload to your webhost that give your WP installation more functionality. For example, if you want to add a contact form to your WP site, you simply install a plugin called Contact Form 7.

If you don't like the default post editor in WP, go get Dean's FCKEditor.

The beauty of plugins is that they offer so much in terms of added functionality, features, or utility without your having to know any code. Plus, they're easy to find – just go to the WordPress Plugin Directory where you can literally find thousands of WordPress plugins.

You can also install plugins directly from within your WP control panel, too. Just go to Plugins –> Add New

That's the nuts and bolts of WP plugins. Now, for the exciting part. What are some good plugins for WordPress? And why?

Here's my list of Essential WordPress plugins, in no particular order:

1. Akismet. The de facto comment SPAM killer. There are others, but this is the standard by which all the others are judged. Part of #6.
2. All in One SEO Pack. This plugin will help you get your SEO in order. Part of #6.
3. cbnet Ping Optimizer. By default, when you publish a post or page on WP, WP "pings" (or notifies) various services, telling them that you've added content. This is good for indexing and SEO purposes. However, WP also sends pings if you make an edit. This is NOT good. I, for example, may make a dozen edits to a post before I move on. WP will have sent 12 pings which could get my site banished from one or more of the pinging services. THIS IS BAD. This plugin eliminates pinging after edits. Part of #6.
4. Dofollow. All my sites are "do follow." This means that any time someone makes a comment on my site, they get a link back to their site that is NOT do not follow, which is the default WP behavior. This is a better backlink for the commenter. I want to encourage comments, even if the commenter only makes a comment to get the "do follow" backlink. I can always trash or SPAM the comment if I don't like it.
5. Easy AdSense. This one makes inserting Google AdSense ads within your posts effortless. You set up your code once and forget about it.
6. Free Traffic Getting SEO. This is a "meta" plugin, in that it incorporates several plugins into one and then sets them up for you so that you derive maximum search engine optimization. You cannot install this one from within WP – you have to upload it to your server.
    Highly Recommended.
   
7. GoCodes. This one is a lifesaver! You can use this plugin to convert an ugly affiliate link into something a little prettier, with tracking. This saves a lot of time and a lot of commissions!
8. Google Analyticator. Inserts the Google tracking code that helps you keep tabs on traffic, keywords, users, etc. Essential!
9. Google XML Sitemaps. Every time you create a page, this plugin re-creates your sitemap and notifies the top 4 search engines (Google, Yahoo, Bing, and Ask). Part of #6.
10. Twitter Widget Pro. I've tried a lot of twitter plugins and this one does what I want – it puts a widget in my sidebar that shows my latest tweets. It does NOT post your blog to twitter. I use HootSuite for that (not a WP plugin).
11. WordPress Backup. This one backs up your themes, uploads, and plugins. Very important. Stores on server and can email you the files.
12. WordPress Database Backup. Even more important than #11. Backs up your WP database, which contains all of your posts and pages. Can store on server or email you the file. Part of #6.
13. Yet Another Related Posts Plugin. Appends related posts from within your own site to the bottom of posts. Great for internal linking optimization.

This is certainly not all of the plugins I use, nor is it a complete listing of every WP plugin you ought to be using. One of the key features of WP's architecture is that multiple plugins can work together, seamlessly, to accomplish a lot of mundane tasks.

However, I will say that once in a while you will run across a plugin that simply doens't work with your existing set of plugins. You'll know it when your site no longer loads. Simply deactivate the offending plugin and find an alternative. Once in a great while, you won't even be able to deactivate a plugin; rather, you will have to use your FTP client to delete its contents from the plugin folder. Ugly, but necessary on occasion.

I hope this list helps you out. These plugins certainly help me a great deal and I use them on every site I create.