Before getting into the best WordPress plugins out there, let’s cover a couple of definitions for the uninitiated among us.

WordPress is the world’s most widely-used open source Content Management System (CMS). While it is often employed as a blog, WordPress is strong enough to run entire websites. So it isn’t just a blogging platform. WordPress is powered by PHP and MySQL, and has exciting features such as templates and plugins that make building fantastic websites relatively effortless. WordPress is used by 13% of the 1,000,000 biggest websites in the world, no small feat considering the breadth of options available.

Plugins are simply applications that augment the capabilities of WordPress and make it better to work with. Most plugins are free.

Here are the best WordPress plugins out there. My opinions are highly subjective, but these are plugins I want you to know about.

#1: All-in-One SEO Pack

The All-in-One SEO Pack makes on-page search engine optimization simple. For this reason, it’s my top pick. With this plugin, adding Meta tags such as title tags, meta descriptions, and keywords has never been easier. This is a good thing, as too many websites are missing these crucial elements (and missing out on online lead generation and/or online sales as a result).

#2: Askimet

Askimet allows you to quit moderating comments. It automatically checks comments left on your website against the Askimet web service to see if they look like spam or not. If it’s spam, they toss the comment out. To keep the service honest, you can analyze the spam it catches to make sure the plugin is doing its job accurately. There are two things that make using this plugin vital. One, your readers will never have to type in a CAPTCHA again. Two, your readers will never have to wait for their comment to be moderated again (this drives me nuts when we visit other blogs).

#3: Google XML Sitemaps

Google XML Sitemaps will produce a special XML sitemap which will allow search engines to index your blog. If that sentence makes your head hurt, just know this: it makes it easier for Google to read your website. That’s a good thing. If Google can’t or doesn’t read your website, that’s bad. You want them to read it so they can share your website with people that use the Internet. Consider this a crucial WordPress plugin if you enjoy trading your labor and/or skills for money.

#4 Subscribe to Comments Reloaded

Consider this one a cherry on the top of your delicious WordPress sundae. Subscribe to Comments Reloaded will change the way people use your blog. Without it, people just stop in, leave a comment, and never return. With this plugin, your readers can click a box saying they wish to be notified of follow-up comments via email. This email notification will (in some cases) cause the reader to return and leave a comment. This will give you more Web traffic, more comments, and it will make your blog more conversational.

#5: TweetMeme

Guy Kawasaki once called this the most important button on the Internet. It probably isn’t at that level today, but it is certainly still highly useful when it comes to getting your message to the masses. Twitter has proven to be a highly beneficial viral marketing tool. If you have something important or interesting to say, odds are Twitter will go a long way in getting your voice heard. Within the Twitter-sphere, there is nothing more valuable than a ReTweet. A ReTweet occurs when someone that reads your content re-broadcasts it to all of their followers. When this happens, viral marketing magic happens. TweetMeme makes it convenient for your blogs’ readers to ReTweet your content, which will bring you more traffic, more comments, and (hopefully) more business.

So there you have it. Those are, in my estimation, the five best WordPress plugins out there.